There really aren't any legal alternatives to iTunes. What there are are sites such as what you found - app shopping aggregators, as it were. That actually looks like a pretty good one. And, there's an app for this site on the App Store, which makes it easier to search.
There are several sites that do this type of service, as well as several apps. Some of the apps that people use are Chomp, Discovr Apps, AppShopper, App Deals, App Smart, AppMiner and too many more to keep listing out.
So, yeah, there's big business in looking for apps. The hardest thing is finding the search tool that works best for you. Hopefully, some of these will work ...
Marilyn