I think the concept drawings (or were these screenshots?) are very nice. I am searching for a tile pixel editor and somehow found this thread.

happymonster: you should update the first post of this thread - at least give it a big, fat link to http://www.retroidea.com/Pixe/ 

I'm on 64bit Linux and wasn't able to make 0.4 run in Wine, I hope that it is portable enough for my platform and that you'll some day release the source.

PS: If you still use Excel for brainstorming, I recommend you upload it to Google Docs and share the read-only link here