The PSP is Sony's entry in the portable game market. Currently it only comes in glossy black or white for the United States market, but one can import other colors from Japan in desired.
It can take a Memory Stick Pro Duo with a capacity of 4 gigabytes out of the box, though that number is doubled after some software updates. The memory stick is the heart of the PSP. On it you store your movies, pictures, and game saves. The PSP can handle a variety of different media formats, so compatibility is not an issue.
The main reason most will buy a PSP, however, is the ability to play games. The PSP has a very large game library, and it is rapidly growing. There are myriads of game types, only hampered by the somewhat subpar control layout. The controls are not a big enough reason to not use the PSP, so it's a very minor flaw. For those on a budget, the PSP has a large selection of "Greatest Hits" games for $19.99.
I bought my PSP at launch and it is still running strong, so the longevity of the console is of no concern.