I'm using the Pichu^2 theme at the moment since it's new, and I want to see if I can grow to like it. Other themes that I use are Forever Standing, Seeds of Platinum, or sometiems PokeLink 4 Blue.
That's one of the things I love about PokeCommunity: The awesome themes. SPPf, Bulbagarden, and other forums just can't compete theme-wise. ;)