http://www.goincase.com/iphone/protectivecover/ I used this before, but since it's rubber the color started to fade off the edges because I kept my phone in my hand so much. It was durable and fit well, until it ripped.
http://www.speckproducts.com/products/pixelskin/iphone-3g-iphone-3gs/143 Then I switched to this, and it's a good case. VERY durable, you could probably throw your phone across the room HARD and nothing will happen to your phone in this case. However, it's a little bulky and I found that the case got a little loose after awhile. Not loose enough to fall off, but enough to wiggle around and irritate me. Visually, I think it's "ugly cute". I did get a lot of attention with this case though, lol.
Now I use this
http://www.goincase.com/iphone/slidercase/! They're great. Thin, nice variety of colors, and good looking protection. It will protect your phone from most falls, but the case will probably break from a really hard fall (but better the case than your phone right?). It's also a little slippery, especially the 'glossy' colors. I would be wary of the 'matte' finishes because it's a coating, and I had a pink matte one and the coating started to chip off, revealing the glossy plastic underneath. I currently have "metallic red" which seems to be discontinued.
I like all three of them and would buy them again. I would get the first one if you want a good grip + protection, and don't mind geting a new cases every 6-8months. The second one is good if your main concerns are protection and grip. The third one is good if you want good looks and decent protection.