Congrats!
Need? I'd get an external hard drive on which to use Time Machine to back everything up, just in case. While I've never had a problem with the stock hard drives in Apple computers, it's better to be safe than sorry... and it also lets you go back in time to retrieve old files, which is a neat trick.
The second thing you should do is go freeware crazy, like me. Start with the essentials, like
Firefox/
Chrome,
Thunderbird,
Skype/
Adium,
Transmission, and
NeoOffice. You may also want to get
VLC,
Flip4Mac and
Perian. You may need to reinstall
flash, as some copies of Snow Leopard (your operating system) are shipping with an outdated version.
Oh, and
GIMP. I've not used it because I have Photoshop, but if you want to save hundreds of $$$ for college, GIMP's a free, lite version.
If you're into games, the 9400m graphics processor is fairly middle of the road, but should be able to handle some games. CoD 4 works well enough (20ish fps) on my friend's 9400m MBP.
If you're looking to get an external monitor or other accessories, I like these:
Acer 22" LCD
Logitech Z-2300 Speakers
Canon Printer
Western Digital External Hard Drive
Let's see... Ah! If, after a lot of use, the MBP is running a bit slower, turn it off, and then turn it back on, holding down option/command/"p"/"r", to zap the PRAM. A lot of non-Mac folks aren't familiar with this, but it does work pretty well to reset some basic settings.
If you've got any questions there are several Mac folks about that would be glad to help, myself included.