I always hated cases and covers and all that, simply because to take away from the beautiful design of the iPhone itself.
With my 2G I never used a case, I used it for about 3.5 years and had it scratch-free for 2.5 years.
But now with my iPhone4 I've got a bumper from Gear4, a leather pouch from some unknown brand and the SwitchEasy Nude.
I always use the SE Nude now, I absolutely love it. I even put on the screen protector. One downside is that the back does get 'greasy', on mine at least.
I have the black one btw.