You can check up The PSP Demo Center, people, such as myself, can upload their own custom themes. The link I posted directly sends you to the Custem Themes section, but you can also check the official PSP themes in the downloads section, as well as find a ton of downloadable demos for your PSP. You can even download my own ICP Theme! Easy to find, it's called "Insane Clown Posse Theme" and the Author is of course "FetusZero". It got posted yesterday and this morning I had 78 hits on it so far which means I'm glad that some people are enjoying it.

The site is also accessible with your PSP if you prefer direct downloads directly onto it, and for once, it's a site that works very well on the PSP.

Just thought I'd tell you all that my theme has been uploaded on the site, and plus you can find other good stuff (such as the demos and many, MANY wallpapers). Some people have real good themes too. I personally really like the "Neon PSP" one, which is the original icons of the PSP but with a neon glow to it, it looks pretty sweet.