You can find some quality windows 7 themes at here.

Just wanted to share with you guys. There are variety of choices available , anime , landscape, nature, movie theme and so on.

For a head start, you can try check it out its Anime themes , Inpirational, and the Nature themes section.

Edit:-
*17/3/2010 - A big post today, 80 stunning wallpapers in one single themepack for all of the users. Guys, please digg, stumble, tweet or facebook share it because this take me some really long time to compile it. Click here to check out all 80 wallpapers
*7/8/2010  - Various interesting themes updates recently, including Final Fantasy, Gundam and STARCRAFT II !!!!!

A " thanks" wouldn't take you more than 2 minutes =). Enjoy the themes.