Psion
Adventurer
Ghostwind said:Gareth hit the nail squarely. Other publishers have created OGL style logos before and offered them freely. Personally, I favor the one created by Mongoose (which also allows any publisher to use it freely) several years ago. But that is just my opinion.
I like the one Grim Tales used. Looked cool, got the idea across more than just "OGL", but "d20 based". Which, if you are shopping for compatibility, is the important part. (OGL is just a license not any sort of set of system assumptions and non-d20 games use OGL.)