I like using ThemeX from mutx.com. It lets you organize, preview, and rotate your themes. I especially like being able to group my themes into different categories since I have about 150 themes (mostly once I
created ). It also lets you use Animated Themes.
Another thing I like about ThemeX is that it comes with a theme creater program for the PPC. It's great for making quick themes directly on your PPC or making adjustments to existing themes. This was actually the first PPC app I paid money for and it's been well worth it.
:D