Searching the App Store using iTunes doesn't work very well, and there are plenty of sites that review apps (including TUAW), but there are so many apps out there that finding what you want can be a matter of luck rather than skill.
That problem has largely been solved with Appsaurus [iTunes link], a U.S. $0.99 app that can quickly focus on what kinds of apps you like and make decent suggestions for new apps to try or buy.
Here's how Appsaurus works. When you launch the app for the first time, it presents you with an explore mode. It displays a list of apps, and you tap the ones that are of interest to you. You may have some of the apps, but you probably won't have all of them. When you select a favorite you'll get a new list that includes apps that match the general description of the app you clicked on. Run through a few iterations of this process, and the app begins to learn your preferences.