there are many different memory sticks you can use for the sony PSP. there is the sony mw duo 32 mb one that it comes with. This is ideal for those users who are just interested in saving video game files and saving a small amount of photos or mp3 files to their PSP.
you can also purchase larger memory sticks (up to 1gb currently) if you are interested in storing more stuff on your PSP. any memory stick with "Magic Gate" written on it should be compatible.
heres an example of an affordable memory stick that would be plenty space for your son to save games on:
(SanDisk SDMSPD-128-A10 128MB MemoryStick Pro Duo)
and here's an example of a memory stick that would be ideal for storing a good amount of songs on it (probably around 240+)
(SanDisk 1 GB Memory Stick Pro Duo (SDMSPD-1024-A10))
good luck with your decision
I was wondering which memory sticks are compatible with the PSP? Please help. My son really wants to play but there is not enough memory.