Agree with Mickey that free apps can be a mixed bag.
Suggestion that's worked well for me: I google a phrase like "best iPad apps" from time to time and have found great free apps that way, by using what I consider good sources for app tipoffs. As a result, I have more than 100 apps that I regularly use, most of them free. I've rarely trawled the app store for apps, because I try to let other people do the finding and testing for me, lol. I look at their lists and cherry-pick from them. (Any decent source will have a blurb explaining what the app does and why it's good.)