For little over a year now I've been using a Mac at work and home, and I've come across some pretty legit programs that have made my life easier.

Fluid: This let's you take any URL and turn it into it's own .app file. It's free, but paying the $5 USD price tag allows you to have your apps have their own cookie storage. (I have Facebook/Twitter/Gmail setup to use Fluid)

Alfred: Assign a global hotkey that'll bring up a prompt to let you type out nearly any command you can think of - use it instead of using your mouse.

Flux: Changes your monitor during sunrise/sunset to the white point you select to make your eyes hate you less.

TotalSpaces: Let's you do all the things you wanted to be able to do with desktop spaces. Being able to assign applications to open up in specific spaces is almost worth the price alone.

iStumbler: See all the wireless access points around you.

Dash: Sometimes you don't have internet and you can't remeber the difference between days_ago and days_since

RSS Notifier: Cool RSS feed notifier that sits in your menu bar. (exportable copy of the feeds i follow)