To me you can't do better than Seidio's Innocase Surface. I have used them on my Blackberriys in the past and I will be getting one for the iPhone 4 just as soon as they get it out.
www.seidio.com
I should buy one for my wife. We had Innocases for our Crackberries. She dropped hers so many times ... on concrete ... and it's still basically flawless. I should probably get her one instead of a Bumper.
I'm using the bumper for now, but prefer a wallet style, slider case. Had one for my 3G/3GS and both survived over a year a piece. I found this site, and was actually surprised by quality and proce. I ordered 6/22 and they promised delivery by 7/14. I'll let you know when it gets here, but seems to be decent.
I ordered a black/red stripe.
www.beyzacases.com
I loved my incase slider on my 3G/3GS and iPod Touch