Of course, there are more free apps than those that appear on the top lists in iTunes. Two websites you can check out for free apps are FreeAppADay and AppShopper.
FreeAppADay is what the name applies. Every day a different app is listed that the developer has agreed to put on sale. Sometimes the sale is a little longer than a day, but if you want that app I would get it the day of the sale. I have found some real gems through this site. However, I must admit most of the apps I have gotten from this site are no longer installed.
AppShopper is a fantastic site to not only finds free apps, but to find new apps and apps on sale also.

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AppShopper tracks new apps, updates to apps, apps that go on sale, paid apps, and free apps. It even has iPad apps. You can subscribe to rss feeds for the category of your choice and find out when a free app is released or when an app goes on sale, etc. Links to iTunes are in each description of the app. I highly suggest checking this site out.