Modified Go
I modified the go program on my server - I added digging and placement, and better yet - loops.

For example "go loop 4 loop 4 fpd 3 r end u end" will build a 4x4 set of walls, 4 high
Spoiler

local tArgs = { ... }
local nArg = 1

if #tArgs < 1 then
	print( "Usage: go <direction> <distance>" )
	print( "Movement: f, u, d, b  Turns: l, r" )
	print( "Digging: df, du, dd")
	print( "Place &amp; move: pb, pu, pd")
	print( "(i.e. place front, move backwards)")
	print( "Move/place - above: pfu  below: pfd")
	return
end

local tMoveHandlers = {
	["f"] = turtle.forward,
	["b"] = turtle.back,
	["u"] = turtle.up,
	["d"] = turtle.down,
	["l"] = turtle.turnLeft,
	["r"] = turtle.turnRight,
	["df"] = turtle.forward,
	["du"] = turtle.up,
	["dd"] = turtle.down,
	["fpd"] = turtle.forward,
	["fpu"] = turtle.forward,
	["bpd"] = turtle.back,
	["bpf"] = turtle.back,
	["bpu"] = turtle.back,
	["upf"] = turtle.up,
	["upd"] = turtle.up,
	["pd"] = turtle.down,
	["pfu"] = turtle.forward,
	["pfd"] = turtle.forward,
}

local tPreHandler = {
	["df"] = turtle.dig,
	["du"] = turtle.digUp,
	["dd"] = turtle.digDown,
}

local tPostHandler = {
	["fpd"] = turtle.placeDown,
	["bpd"] = turtle.placeDown,
	["upd"] = turtle.placeDown,
	["pd"] = turtle.placeDown,
	["pfd"] = turtle.place,
	["bpf"] = turtle.place,
	["upf"] = turtle.place,
	["fpu"] = turtle.placeUp,
	["bpu"] = turtle.placeUp,
	["pfu"] = turtle.placeUp,
}

function doLoop(count, argStart)
	for i = 1, count do
		nArg = argStart
		doAction()
	end
end

function doAction()
	while nArg <= #tArgs do
		local sDirection = tArgs[nArg]
		local nDistance = 1
		if nArg < #tArgs then
			local num = tonumber( tArgs[nArg + 1] )
			if num then
				nDistance = num
				nArg = nArg + 1
			end
		end
		nArg = nArg + 1
	
		if (sDirection == "loop") then
			doLoop(nDistance, nArg)
		elseif (sDirection == "end") then
			return
		end
		
		local fnHandler = tMoveHandlers[string.lower(sDirection)]
		if fnHandler then
			local fnPreHandler = tPreHandler[string.lower(sDirection)]
			local fnPostHandler = tPostHandler[string.lower(sDirection)]
	
			for n=1,nDistance do
				
				if (fnPreHandler) then
					fnPreHandler()
				end
				
				fnHandler( nArg )
	
				if (fnPostHandler) then
					fnPostHandler()
				end
			end
		end
	
	end
end

doAction()

State API
I realize there's some other state Apis - I've been enjoying making my own libraries - I'm sharing them here mostly so the other programs I post will work

Spoiler

local statePath = "/state/"

if not fs.exists(statePath) then
	fs.makeDir(statePath)
end


function init(module, variable, defaultValue)
	fileName = statePath .. module .. "/" .. variable

	if not fs.exists(statePath .. module) then
		fs.makeDir(statePath .. module)
	end

	content = defaultValue
	
	if (fs.exists(fileName)) then
		content = get(module, variable)
	else
		set(module, variable, defaultValue)
	end
	
	return content
end

function set(module, variable, value)
	fileName = statePath .. module .. "/" .. variable
	
	file = io.open(fileName, "w")
	if (file) then
		file:write(value)
		file:close()
	else
		
	end
end

function get(module, variable)
	fileName = statePath .. module .. "/" .. variable
	
	content = nil
	
	if (fs.exists(fileName)) then
		file = io.open(fileName, "r")
		content = file:read()
		file:close()
	end
	
	return content
end

function clear(module, variable)
	fileName = statePath .. module .. "/" .. variable
	
	if (fs.exists(fileName)) then
		fs.delete(fileName)
	end
end

tMove API
My personal movement library

Spoiler

os.loadAPI("rom/apis/state")
local module = "tMove"

local xPos = tonumber(state.init(module, "xPos", 0))
local yPos = tonumber(state.init(module, "yPos", 0))
local height = tonumber(state.init(module, "height", 0))
local xDir = tonumber(state.init(module, "xDir", 0))
local yDir = tonumber(state.init(module, "yDir", 1))

local function _setPos(x, y, h, xD, yD)
	xPos = x
	yPos = y
	height = h
	xDir = xD
	yDir = yD
	
	state.set(module, "xPos", xPos)
	state.set(module, "yPos", yPos)
	state.set(module, "height", height)
	state.set(module, "xDir", xDir)
	state.set(module, "yDir", yDir)
end

function setPos(x, y, h, xD, yD)
	_setPos(x or 0, y or 0, h or 0, xD or 0, yD or 1)
end

function getPos()
	return xPos, yPos, height, xDir, yDir
end

function turnLeft()
	turtle.turnLeft()
	xDir, yDir = -yDir, xDir

	state.set(module, "xDir", xDir)
	state.set(module, "yDir", yDir)
end

function turnRight()
	turtle.turnRight()
	xDir, yDir = yDir, -xDir

	state.set(module, "xDir", xDir)
	state.set(module, "yDir", yDir)
end

function setFace(tXDir, tYDir)
	while ((tXDir ~= xDir) or (tYDir ~= yDir)) do
		if ((xDir == tYDir) and (yDir == -tXDir)) then
			turnLeft()
		else
			turnRight()
		end	
	end
end

function forwardOne()
	local success = turtle.forward()
	
	if (success) then
		xPos = xPos + xDir
		yPos = yPos + yDir
		
		state.set(module, "xPos", xPos)
		state.set(module, "yPos", yPos)
	end
	
	return success
end

function forward(count)
	while (count > 0) do
		if (forwardOne()) then
   		 count = count - 1
		end
	end
end

function upOne()
	local success = turtle.up()
	
	if (success) then
		height = height + 1
	
		state.set(module, "height", height)
	end
	
	return success
end

function up(count)
	while (count > 0) do
		if (upOne()) then
   		 count = count - 1
		end
	end
end

function downOne()
	local success = turtle.down()
	
	if (success) then
		height = height - 1
	
		state.set(module, "height", height)
	end
	
	return success
end

function down(count)
	while (count > 0) do
		if (downOne()) then
   		 count = count - 1
		end
	end
end

function heightTo(tHeight)
	dist = math.abs(tHeight - height)
	dir = (tHeight - height) / dist
	
	if (dir == 1) then
		up(dist)
	else
		down(dist)
	end
end

-- This function should move the turtle to the specified coordinates
-- xPrimary is a true/false value which should represent which axis to move along first.
-- If true, x Axis will be used first, otherwise Y
function to(tX, tY, xPrimary)

	local dist = 0
	
	if (xPrimary and (tX ~= xPos)) then
		dist = math.abs(tX - xPos)
		dir = (tX - xPos) / dist
		setFace(dir, 0)
		forward(dist)
	end
	
	if (tY ~= yPos) then
		dist = math.abs(tY - yPos)
		dir = (tY - yPos) / dist
		setFace(0, dir)
		forward(dist)
	end
	
	if (tX ~= xPos) then
		dist = math.abs(tX - xPos)
		dir = (tX - xPos) / dist
		setFace(dir, 0)
		forward(dist)
	end
end

function displayPos()
	print("X: " .. xPos .. " Y: " .. yPos .. " H: " .. height)
	print("XDir: " .. xDir .. " YDir: " .. yDir)
end

Pave
I've used this to make floors of a tower, and then go back over it and place torches.

It operates left to right - in the direction it is facing to start. It does not handle state changes (reboots, etc)

Spoiler

Frame Eater
This will 'eat' a buildcraft frame. (After it's done) Dig out the bottom left corner of the frame and place the turtle there. As long as there are no oddities in the frame (blocks placed within the frame area, etc), it will learn how large the frame is and dismantle it for you

Spoiler

os.loadAPI("rom/apis/turtle/tmove")

local module = "frameEater"

tMove.setPos(0, 0, 0)

local xPos, yPos, height, xDir, yDir = 0, 0, 0 , 0, 0
local stage = 1

local maxX = 0
local maxY = 0
local maxH = 0

local tArgs = { ... }

-- Stage 4
local function home()
	print("Going home")
	tMove.heightTo(0)
	tMove.to(0, 0, true)
	tMove.heightTo(0)
	tMove.setFace(0, 1)
end

local function getPos()
	xPos, yPos, height, xDir, yDir = tMove.getPos()
end

local function mineToNextVertical()
	repeat
		turtle.dig()
		tMove.forward(1)
		getPos()
		
		if (turtle.getItemCount(9) == 64) then
			return false
		end
	until turtle.detectUp()
	
	return true
end

local function mineUpToHorizontal()
	repeat
		turtle.digUp()
		tMove.up(1)
		getPos()
		
		if (turtle.getItemCount(9) == 64) then
			return false
		end
	until turtle.detect()
	
	return true
end

local function digUp(count)
	while (count > 0) do
		turtle.digUp()
		tMove.up(1)
		count = count - 1
		getPos()

		if (turtle.getItemCount(9) == 64) then
			return false
		end
	end
	
	return true
end

local function digForward(count)
	while (count > 0) do
		turtle.dig()
		tMove.forward(1)
		count = count - 1
		getPos()

		if (turtle.getItemCount(9) == 64) then
			return false
		end
	end
	
	return true
end

while ((stage > 0) and (stage <= 12)) do
	print("Main loop - stage: " .. stage)
	state.set(module, "stage", stage)

	if (stage == 1) then
	   -- Mine to the first vertical
	   if (mineToNextVertical()) then
		   maxY = yPos
		   tMove.turnRight()
		   stage = stage + 1
	   else
		   return
	   end
	elseif (stage == 2) then
	   if (mineUpToHorizontal()) then
		   maxH = height
		   tMove.heightTo(0)
		   stage = stage + 1
	   else
		   return
	   end
	elseif (stage == 3) then
	   -- Mine to the first vertical
	   if (mineToNextVertical()) then
		   maxX = xPos
		   tMove.turnRight()
		   stage = stage + 1
	   else
		   return
	   end
	elseif ((stage == 4) or (stage == 6)) then
	   if (digUp(maxH)) then
		   tMove.heightTo(0)
		   stage = stage + 1
	   else
		   return
	   end
	elseif (stage == 8) then
	   if (digUp(maxH)) then
		   stage = stage + 1
	   else
		   return
	   end
	elseif ((stage == 5) or (stage == 9) or (stage == 11)) then
		if (digForward(maxY)) then
			tMove.turnRight()
			stage = stage + 1
		else
			return
		end
	elseif ((stage == 7) or (stage == 10) or (stage == 12)) then
		if (digForward(maxX)) then
			tMove.turnRight()
			stage = stage + 1
		else
			return
		end
	end
end

home()