I recommend & love the following applications:

AdiumX (best instant messenger ever)

Aperture 2 (for photographers)

BetterZip (great unpacking application)

CandyBar (change the look of your OS X, use http://macthemes2.net as a great resource)

Coda (for webdevelopers, awesome!)

Colloquy (best IRC client)

Little Snitch (must need for all of us)

OmniWeb (perfect Browser, I love it even more than Safari now!)

SubEthaEdit (best Editor for text and all kind of programming languages)

Speed Download (nice Download Manager)

Transmit (best SCP/FTP Client)

TeXShop (LaTeX!)


Have fun (you certainly will)!