Did you know that you can play Echochrome in Playstation Home? It's not the same as the one on the PSP demo. I think it's actually much more challenging. Anyway, if you're interested, you can find it in the arcade at the bowling alley in Playstation Home (which is free, but takes about 3 GB of HDD space).
Oh and you might also like the Carriage Return game in the arcade also.
I just wish the arcade games were a little easier to start. They are a little tricky because you have to be in just the right spot when you hit the Play button, otherwise it doesn't actually start.