I've been using a Speck Pixel case. It's not really a hard case, but it's not a soft rubbery one either - sort of in between. I really like it. It covers the sides and back as well as having a tiny lip over the front, so that if the phone is dropped on a flat surface the screen will never be touched.
I've dropped my phone a couple of times and have not one scratch with this case. They have quite a few colors and they are fairly easy to snap on and off and to keep clean. I don't see people talk about them too much which surprises me, but I definitely recommend them. They are not bulky, IMO.