A simple random map generator using seeding and growth to produce it's landmasses.

MapGenerator.py

import Image, random, math
#Made by pbsds/Peder Bergebakken Sundt
#Requires PIL to work

Palette = (0x0045A0,#0 - Dark water
  	   0x0059BC,#1 - Water
		   0x0078F9,#2 - Shore water
		   0xFFF65E,#3 - Sand
		   0x2BE81F,#4 - Grass
		   0x26B719,#5 - Dark Grass
		   0xA8712F,#6 - Mountain foot
		   0x7F3300,#7 - Mountain side
		   0xA8865C,#8 - Mountain top
		   0xCEA471,#9 - Mountain peak
		   0x006B0A,#10- Tree
		   0xFF0000)#11- City

def Random(i1, i2):
	if i1 == i2:
		return i1
	return int(random.randrange(i1,i2))
def TryInt(i):#tries to convert to int, if possible
	try:
		return int(i)
	except:
		return i
def CircleOffsets(Radius):
	ret = []
	for y in xrange(-Radius-1,Radius+1):
		for x in xrange(-Radius-1,Radius+1):
			if math.sqrt(x**2 + y**2) <= Radius:
				ret.append((x, y))
	return ret
def DecAsc(dec,pad = -1):#Converts a decimal into an ascii string with the specified padding(Big Endian)
	ret = ""
	while dec <> 0:
		ret = chr(dec&0xFF) + ret
		dec >>= 8
	if pad <> -1:
		if len(ret) > pad:
			ret = ret[:pad]
		if len(ret) < pad:
			ret = "\0"*(pad-len(ret)) + ret
	return ret
def SaveImage(Map, OutputPath = "out.png"):
	global Palette
	w = len(Map)
	h = len(Map[0])
	data = []
	for y in range(h):
		for x in range(w):
			data.append(DecAsc(Palette[Map[x][y]],3))
			#data[x+y*w] = DecAsc(Map[x][y],3)
	data = "".join(data)
	
	img = Image.fromstring("RGB", (w, h), data)
	filetype = OutputPath[OutputPath.rfind(".")+1:]
	img.save(OutputPath, filetype)
	
print " - pbsds's map generator -"
print "The values inside the parentheses are my personal preferences during testing."
random.seed(TryInt(raw_input("Insert psuedo-random seed(1337): ")))
Chance    = input("Insert land-spread chance percentage(99): ")
Seeds     = input("Insert number of inital land-seeds(20-30): ")
Frame     = input("Insert border padding size for thhe land-seeds(0): ")
MapWidth  = input("Insert output image width(400-500): ")
MapHeight = input("Insert output image height(400-500): ")

print "Generating the land masses..."
Check = []#the pixels to work with
Map = [[None for y in xrange(MapHeight)] for x in xrange(MapWidth)]#None = Unset, or the indexes from Palette
WidthRange  = range(MapWidth)
HeightRange = range(MapHeight)

#inital land-roots:
for i in xrange(Seeds):
	x = Random(Frame, MapWidth-1-Frame)
	y = Random(Frame, MapHeight-1-Frame)
	Map[x][y] = 5#dark grass
	Check.append((x,y))

#Create the landmasses:
while Check:
	x, y = Check.pop(Random(0,len(Check)-1))
	
	for x2, y2 in ((x-1, y-1), (x, y-1), (x+1, y-1), (x+1, y), (x+1, y+1), (x, y+1), (x-1, y+1), (x-1, y)):#For each neightbor:
		if not (x2 < 0  or x2 >= MapWidth or y2 < 0  or y2 >= MapHeight):#If within the map:
			if Map[x2][y2] == None:#If neighboring pixel isn't set yet:
				#if current pixel is water, set neightboring pixel to water.
				#if it's land, set the neightboring pixel to either land or water chosen randomly
				if Map[x][y] == 0:
					Map[x2][y2] = 0#water
				else:
					if Random(0,100) < Chance:
						Map[x2][y2] = 5#grass
					else:
						Map[x2][y2] = 0#water
				Check.append((x2,y2))

print "Removing 1x1 sized lakes..."
for y in HeightRange:
	for x in WidthRange:
		if Map[x][y] == 0:
			Remove = True
			for x2, y2 in ((x+1,y), (x-1,y), (x,y+1), (x,y-1)):
				if 0 <= x2 < MapWidth and 0 <= y2 < MapHeight:
					if Map[x2][y2] == 0:
						Remove = False
						break
			if Remove:
				Map[x][y] = 5

#Colour the map:
print "Colouring the map..."
Radius1 = CircleOffsets(4)
Radius2 = CircleOffsets(13)
for i in Radius1:
	Radius2.remove(i)
Radius1.remove((0,0))

for y in HeightRange:
	for x in WidthRange:
		if Map[x][y] in (4, 5):
			#Check if by the water:
			for x2, y2 in ((x+1,y), (x-1,y), (x,y+1), (x,y-1)):
				if 0 <= x2 < MapWidth and 0 <= y2 < MapHeight:
					if Map[x2][y2] in (2,1,0):
						#Add the sand shore:
						Map[x][y] = 3#sand
						
						#Add Bright water along the shore:
						for x2, y2 in Radius1:
							if not (x+x2 < 0 or x+x2 >= MapWidth or y+y2 < 0 or y+y2 >= MapHeight):
								if Map[x+x2][y+y2] in (0,1):
									Map[x+x2][y+y2] = 2#Shore water
						
						#add deeper water further out along the shore and lighter grass:
						for x2, y2 in Radius2:
							if not (x+x2 < 0 or x+x2 >= MapWidth or y+y2 < 0 or y+y2 >= MapHeight):
								if Map[x+x2][y+y2] == 0:
									Map[x+x2][y+y2] = 1#normal water
								elif Map[x+x2][y+y2] == 5:
									Map[x+x2][y+y2] = 4#light grass
	
#Finishing the work:
print "Saving as png...",
SaveImage(Map)
print "Done!"

This is my take on http://www.cartania.com/alexander/generation.html