My wife and I have had (or will have had) around 6:
For wife:
1) Red Rocketfish silicone cover, didn't fit well, so returned it.
2) Incipio - pink silicone cover thing that came in a 2 pack from the AT&T store, received this free from a friend.
3) Incase Smoke Snap Case - free from case program, haven't received it yet.
For me:
1) Apple Bumper - bought launch week and was refunded by Apple (currently on my phone)
2) Incase Slider - should be here sometime next week
3) Otterbox Defender - $19.84 from Amazon, not sure when it will get here.
Also, to provide cheap screen protection, I took one of the antimicrobial silver micro fiber clothes you get in the iKlear package, and sewed it into a sleeve/sock thing. It is a tight fit with the bumper on, but it provides great protection, and you always have a micro-fiber handy.
Also, had surgery yesterday, so I am on pain-killers, hope this all makes sense.