Here's what I've bought so far...
Utilities
Beautiful Widgets - I like the settings widgets better than the HTC ones and I like the small version of the clock.
Startup Auditor - stops crap like Qik and all the Sprint apps from starting up with my phone and also gives you the option to disable them from opening themselves up at random. No longer do I go into System Panel and find Qik and Sprint Nav and Sprint Zone open and running in the background 20 minutes after I killed their task previously.
SystemPanel - I bought this because I found the Lite version so useful and I wanted to show my support to the creator. The pro version also allows you to install and uninstall apps and back them up. I used to use AppMonster and AppInstaller which are free, but now System Panel for everything.
Games
WordWise Pro - I love playing Words With Friends on my friends iPhone, and this is pretty much the same thing (Scrabble) on Android. I played the hell out of the free version and bought the Pro version to show my support and get rid of all of the ads. They have said that once they get the Android version to 100% done, they might start an iPhone version too so that we can play cross-platform. Very cool, especially since Words With Friends isn't showing Android any love.
Robo Tower Defense - I love tower defense games and this is the best one on Android.
Abduction World Attack - I loved Doodle Jump on my friends iPhone, but the game is a mess on Android (platforms run out constantly or you get a jetpack to no where). Abduction is the same concept but with a lot more features. There are like 20 different levels in adventure mode where you can unlock new characters. Then there is like single play mode where you can choose a difficulty and try to make it to the top
On The Bubble
Shoot-U - I've thought about buying this one because I like the Lite version, but I haven't pulled the trigger yet for whatever reason
Doodle Jump - probably my favorite game on the iPhone. It is $3.50 which is a rip-off compared to the 99 cent iPhone version. Also, unfortunately the Android version is pretty much unplayable. It seems like every time I set a high score all of the platforms disappear. You'll literally jump up and there will be nothing, no monsters, no platforms and you die. Or you get a jetpack or a trampoline and they just drop you off in empty space with no platforms above or beneath you and you die. There was supposed to be a huge 4th update at the end of June so I was going to buy it then, but the update hasn't come out yet.