You need an Apple Keyboard if you want to operate the OS properly (you can get away with something else, but it's painful). I prefer the full size keyboard (wired), but that's just me. Performs just fine for everything I need.
A Magic Mouse is only useful if you use MagicPrefs:
http://magicprefs.com/ - allows you to customize the mouse gestures to something that makes more sense then the default Lion ones.
If you want to game at all, I really recommend just getting a wired Logitech mouse. Driver support is pretty good and it's hard to beat Logitech mice right now. The Magic mouse is great for everything BUT gaming.