I love cases as much as the iPhone itself and I've become very picky over the years.
Here is the list of what I have and my Top 5 cases:
Number 1: IvySkin Quattro T4 case:
iphone 3GS ipod touch 2g cases Hard iPhone 3GS case iphone battery case
By far the best case I owned. It's design, finish, slim profile and best of all the glass screen guard makes this case my #1 choice
Number 2: Speck CandyShell case:
Speck | CandyShell Case for iPhone 3G & iPhone 3GS
Ranked 2nd because it doest have a hard screen guard and it scratches after couple of weeks.
Number 3: Vaja leather case:
Vaja Leather Products
#3 Because after using it for 3 months, the belt-clip broke. For such a high priced item, I expected somthing better. Overall a great case though.
Number 4: Otterbox defender:
iPhone 3G / 3GS Defender Case // OtterBox.com
I bought this case before I found out about the IvySkin T4 case. This was great before I got the T4. IvySkin case provides the same protection but is slimmer and has a glass touch screen so that's why this is ranked #4.
Number 5: Switcheasy case:
Welcome to SwitchEasy
This was a great case for only a week. After the first week, the bottom of the case became loose and looked awful. I contacted them and they sent a new one.... I had the same issue. It looks great but I hated the hanging skin on my slick iPhone.