Trying to decide on a project

I can't think of any fun/challenging projects to do in C#.

Anyone got ideas?

I've done a chat server/client, Diablo II text OCR, B.Net tourney manager with PHP interface, infix -> postfix converter, 2D RPG engine, and lots of little bits of D2 bots back in the day.

I'd like to think I'm upper level beginner/intermediate.

I haven't really used generics, or lots of nifty features of C#, a project including those would be gravy.