I've been using those two a lot as well as OmniFocus for the iPhone and the desktop client. So far, so good. I always have my iPod Touch with me, so I'm capturing my ideas about current and future projects for work. I've been using it a lot in the last week and I can't tell you how much it's changed my life.
The software is based on the book "Getting Things Done" by David Allen...it's changing how I do everything, in a very very good way.
Other than that, the paid apps I like are:
iDrink
a Dice Poker Game
Koi Pond (I know, lame and silly, but it's fun)
I've got tons of free apps, some which I still have on the phone and others I don't anymore, mostly free games.... ChartFight is a free game that's essentially a Battleship ripoff. The cool thing is that it can discover other iPhone/iPod Touch users nearby (via WiFi) and you can play them remotely. My wife and I had fun playing that game.