Don't know if you're a programmer or not but if you are you will love TextWrangler, or the shareware TextMate. SubEthaEdit and Smultron are good too but TW is my favorite.
Other useful freebies:
FTP: Cyberduck
Bittorrent: Transmission
Chat: AdiumX
File management (where'd all my free space go?): Disk Inventory X / Grand Perspective
Wifi finder: iStumbler 2
Application launcher: Quicksilver
Nocturne -- cool little app when you're working at night and don't want to disturb the roommate
DC++ client: Shakespeer
Pay apps:
iConquer -- great RISK-like game
Disco -- excellent, simpler alternative to Toast for CD/DVD burning
MacHeist -- a website that offers insanely good deals on shareware bundles from time to time
Apple users are lucky there is such a vibrant developer base interested in creating polished, simple and easy to use applications for free or for small amounts of money. We use Macs at work for everything from programming to media creation and we pretty much never need to boot Windows for anything. I'm sure you will love your Macbook Pro. My Powerbook G4 has seen me through part of high school and college and I think I'm going to be getting a few more years of good use out of it.