Nothing but Nokia themes it is.. I actually went throught all 38 pages of Nokia E61 themes lol ..I even downloaded this halloween theme to get in spirit ...
There is also software, games and more..some free..some trials.. enjoy..
NOTE: If you get tired of a theme and want to remove it - you'll notice that there isnt a delete or remove option in themes..
Go to Menu -> Tools -> App.mgr. here you can select and remove themes.