Underappreciated Asset: Power Stone Collection (PSP)
There were 859 games released for the PSP during it's lifetime. Not all of them were North America releases, but regardless 859 is a staggering number. What is interesting is that very few PSP releases have become valuable. In general, I think PSP games are under-recognized by collectors. There are a ton of interesting games, a bunch of RPGs, and numerous games by interesting publishers (ATLAS, Capcom, etc.). It's weird - the system was supported for many years but never seemed to be all that popular. So none of the releases seem to have large print runs or high eBay volume. I'm picking Power Stone Collection here, but I could pick any number of other games for the system.
Power Stone 1 and 2 were arcade and Dreamcast releases until 2006 when Capcom released this game for PSP. The games are pretty universally loved. This release has both games on one disc, which makes it a great value. And the game has somehow never seen an XBL or PSN release. Power Stone games are known for fun multiplayer, and an unfortunate downside with this release is that you can only play multi if you have friends around with both a PSP and a copy of the game.
This can be tricky, because 11 years after its release the game is not easy to find - especially CIB. Right now there are only three CIB copies listed on eBay. The good news is that although the game appears to have somewhat dried up, you can still buy it pretty cheap. Expect to pay in the $20-30 range for a complete copy and $10-15 for a loose copy. Not bad for a beloved Capcom franchise, with Dreamcast versions valued at $130-$150 for the pair.