Early on, when the number of iPhone apps was in the thousands, the App Store was a good way for users to find apps and for developers to bring their apps to the attention of users. Now that there are over 200,000 apps, the App Store isn't that helpful.
When you do a search on a topic in the iTunes store, you might get hundreds of results. They are displayed in no particular order and there is no way to sort them according to most popular, best-selling, free vs. paid, etc. The 20 broad categories also aren't that useful, since there are so many apps that don't obviously fit any particular category. Fortunately, the Internet can help. In this article, I'll point you to some useful lists of the best apps.