I managed to pick this app up when it was initially released for free, now it runs $2.99, but I would still pay for it. Zenbe is a pretty straight forward list tracking app that allows you to create multiple lists, assign due dates and organize your items. It has the added bonus of having a pretty decent web front end that stays in sync at lists.zenbe.com
I continue to find Yelp very useful when looking for new restaurants and bars, the iPhone app is a nice compliment to the website.
I am pretty much addicted to iPhone solitaire, this version is great. They have a free version as well, but I think its worth the price for the added game variations you get.
I kinda hate to admit it, but I check Facebook on my phone way more than I probably need to be.
Mint is a great tool for tacking your expenses and investments, the iPhone application makes it even more useful.
I still thing Evernote is a great tool, I just don't use is at much as I should.
Shazam is one of the most clever apps I've seen. It has been able to identify songs in some pretty poor audio situations.
GasBag crashes way more than a public application should, but I do like the MPG tracking component of the application.
Remote is still a great app for controlling your music from anywhere in your house, even if your house is really only about 750 sq. feet.