While a 256MB Memory Stick may not hold a lot of data, especially if you're trying to play full-resolution movies on your PSP, it's hard to argue about something's worth when it's free. And right now Circuit City is offering a 256MB SanDisk Memory Stick Pro Duo for $30 with a $30 mail-in rebate.
All you have to do is buy the Memory Stick, fill out the form and mail it in. Not too hard, eh?
There's a one-rebate limit here so don't get any funny ideas of buying tons of these and unloading them on ebay.