adium for aim
butler for a means to open any app by just typing. I've heard quicksilver is good too, haven't tried it.
Keep safari for your web, mail for your email
VLC for watching things quick time doesn't play. VLC will also play any region DVD, by the way. Just disable the auto-run of DVD player in your system settings.
I don't know how much or if ever you look up japanese words, but JEDict is an awesome dictionary program. I didn't stumble upon it at first, but its damn great.