I'm using Photoshop to start creating a tileset... I wanted to work with one layer per tile, with layer masks, etc. but didn't want to do that effort manually times 256. So I made a script.
Calling the script will create a new image with 256 layers, each with the appropriate mask and tile name. It leaves a white background layer, which you can either delete or fill with some other tileset that you want to work over. Anyone using photoshop should know how to do that already. Also, you'll have to export as png to get something usable for game.
I am not certain I have tile names correct, so if you see errors there, please post corrections. Also, there is little to no error checking, so if you run into errors, post details here.
Finally, my instructions above are for Mac; I don't have Windows nor Windows PS to test. If Windows/PS users run into problems, check out the scripting documentation: