ADW or LauncherPro; the choice is yours. If you want to do more:
Root your phone.
Install custom ROMs. I liked Cherry Pi a lot, and while finicky occasionally, it's pretty solid. (More stable than the stock Froyo ROM, about on par with the stock Gingerbread ROM unless you are mucking with things you shouldn't be). You should still try it out because of all of the robustness it adds, like 1080p video recording.
http://forum.xda-developers.com/showthr ... ?t=1189497
Do not confuse this ROM with CherryBLUR. That ROM is intended for international Atrixs only (meaning use it if you live outside the US).
Other than that, a lot of it is up to you. Themes are personal preference.
As a real hardware forum, I shouldn't recommend emulators. But really, it's fine if you're not trying to emulate PSX or N64. The Tegra 2 chip is nice, so use it well.
I almost forgot about keyboards though. Better Keyboard and Swiftkey are awesome. But really, I don't mind the stock Moto keyboard. It's not in custom ROMs, and the stock Android keyboard, while not terrible, needs improvement.