I've had an iPad 2 for around a year, and for those of you new to the tablet, I'd really advise against getting a screen protector. The only thing they do is make the quality of the screen look worse. You do not need a screen protector. Short of taking your keys to it, it ain't gonna scratch.
Personally, I do have a shell (cover/case for the back) that looks similar to this one:
I'd totally recommend one, not mainly because of protecting the back from scratches, but because I find the back of the iPad to simply be slippery, especially when you're resting it on even slightly polishes surfaces (wood, plastic, etc). Shop around to see which plastic material you find offers the best grip and look.
I also own an Apple Smart Cover, just because of its convenience. On the off chance that a maniac takes a key to the screen (or a drink spills in my bag or whatever), it's pretty well protected, but it's also super convenient for use as a stand. It's definitely not necessary, but I enjoy the perks it brings.
But yeah, totally recommend the back case, totally don't recommend any kind of film screen protector.