I agree...GetJar, Amazon are pointless which take up space and bog down your system. Just go with the built in app store and task manager. People in here have different views, I find the best way to get acclimated to your phone is to just play with the thing and read the sticky notes. There are tons of threads floating around out there to give you what you need.
I don't know anything about GetJar, but I disagree about Amazon. It's not a big app, taking up only about 6.5MB on my phone. Most of the free apps are lame games, low rated and sluggish. They are free, though. I have it because there are many days when the free app is fantastic, be it a great game or an excellent utility or office suite. Here are a few examples: Bejeweled 2, Abduction2, Cut the Rope, Fieldrunners, Chuzzle, Fancy Widget Pro, Frogger, Jenga, Angry Birds (add free), PacMan, Paper Camera, PrintShare Mobile, App 2 SD Pro, Documents To Go, Office Suite Pro 5, WiFi File Explorer Pro, PicSay Pro, Plants vs. Zombies, Quickoffice Pro, Pocketbooth, SwiftKey X...
I have about 120 apps in all. I don't get the app every day because I just don't want or need all of them. But the ones I have gotten total up to nearly $350. Not bad for free. Especially some of the utilities and office suites they have. These aren't bull apps developed by hack programmers - they are the same apps on the Marketplace and full versions, at that.