software
I use:
Caffeine (free& stays in your menu bar for easy access) - stops your monitor from dimming which is good for when you're being productive editing a paper stay idle (away from keyboard or mouse) from longer than average periods of time.
DropBox (free & stays in your menu bar): 2gigs of online storage. Easy to use and understand. Mounts just like a regular file and automatically backs up everything you throw in there. I can "recommend e-mail" this to you and you and I will get an additional .5gigs of space. 🙂
Things ($50): Great Task Management software. I use it multiple times a day. Syncs up with iCal (which you can sync with Google Calendar), and allows you to print a nice foldable ToDos page.
iTunes plugin - iConcertCal (free): scans your music and allows you to bring up a cool calendar of concerts that reflects your iTunes music.
Sequential (free): Better image viewer. Better for viewing galleries, if you're not using iPhoto. Make it your default, I did.
VLC Player (free): Plays everything and has network capabilities for streaming from a network drive or another computer. Not to mention, it plays EVERYTHING you throw at it.
AppCleaner or another Application Clean up: Makes sure when you delete an App, it takes EVERYTHING it brought away with it.
Skype (free): If you have a camera. Some people think it works better than iChat -- me included -- not that i'm some expert -- I'm not.
OpenBravo (free & open source): If you're planning on running a restaurant or store. It's a free Point of Sales software that is ready for touch screen. It's pretty tight.