Purchase beautiful widgets, very nice! If you like Launcher Pro, I would suggest purchasing the Plus version, the sense like widgets it adds (facebook, people, calendar, bookmarks, twitter, etc) and the ability to costumize dock icons and the dock background as well as resizing widgets is fantastic!
FYI is you install a 3rd party launcher be sure to clear all the screens on the default home screen or you will have your phone running double time.
Another free favorite app is Quick Settings, I like that you can set it to be in the notification bar but be invisible until you drop down the bar then you can access, bluetooth, wifi, brightness, ringer settings, you name it as you can select which items show up in the pop-up screen.
Astro File Manager is a good app to have as it allows for more control than the stock file explorer.
If you liek music check out DoubleTwist player and TuneIn Radio as well as Music Downloader (all free).
For sports I like Sportstap as I prefer their widget over ScoreMobile but check them both out. ESPN is good but no widget.
I am a snowboarder so the new SkiReport app is great, still nothing from OnTheSnow but this one suffices.
Check out AppBrain too, it's like the market on crack.
I purchased MyBackup Pro but that's becuase I have had a phone stolen and like that I can back up my apps, settings and pictures on my sd card and online.