iPod Touch 4G case recommendations
I've been using this case since the day I got mine back in June of 2011.

Its very robust, it completely covers the screen, and I have never had problems tapping the edge.
One thing you do need to be aware of though is the clip. In the picture its shown as being on the back, however I've found that to be somewhat unreliable. If you switch it around to the front (so the clip is covering the screen), its much better.
One of the (in my opinion nice) side benefits of using this case is it adds enough mass to it that you don't have to worry about the iPod just slipping out of your hand - for the week I used mine without a case, I found that it was almost too light and thin, and I kept fearing that the iPod would just fly out of my hand. Its a full body case (as you can see), so while you can't drop it into water (or a blender) and have it be fine, you can drop it a few times and it'll still be OK (handy for those first few times the belt clip fails until you learn the best way to use it! ;)