Heh didnt notice others have already made these, but heres another (btw Phaelax my image blender says it will kick your image blenders ass).
I got tired of mucking around in photoshop, so I just wrote a simple little program that blends two images together. Youll get 3 exported images ideal for terrain tilesets. A straight vertical blend, a inner corner blend and a outer corner blend. Its pretty easy to tweak the code to get a blend for every 8 sides, but these 3 are really enough if you just use rotation.
I tested a couple different combos and most looked perfect, but one or two looked a little funky. Let me know if you get any buggy results.
Enjoy!
All you need is zeal