Otterbox defender probably has the best drop protection. I also like the looks of the iSkin Revo4. It looks like it provides nice protection as well. There are also Ballistic Cases which are supposed have nice protection and there is the Case-Mate tough, which is really just a hunk of silicon. The Speck Candyshell is a nice case as well offering sufficient drop protection while still sliding in an out of your pocket. Or, you might like the look of the Speck Toughshell.
Otterbox Defender
iSkin Revo4
Ballistic Cases
Case-Mate Tough
Speck Candyshell
Speck Toughshell
It looks like the Defender has a built in screen protector. Will the defender work if I have a PowerSupport anti-glare screen protector already installed on the iphone 4?
Yes but it may leave permanent impressions on it after you remove the phone from the case.
What do you mean?
If you're worried about scratches than order a few screen protectors off ebay and slap it on your screen before you use the Defender. I do it and it works fine and my screen is scratch free.Ive heard the defender gets dust and particles under the screen cover which can cause scratches to your screen.?