I always get my cases from Amazon
when I don't get them as gifts. They are SUPER inexpensive, and actually hold up pretty well; as long as you get the right ones. So I'm going to suggest you head there first.
My best guy friend got me my current case, and it's definitely my favorite. It's super cute, feels great in my hand, and holds up really well. I'm VERY hard on my iPhone, and it hasn't got a single crack on it. Unfortunately, I have no idea what brand it is, but it was a $30 case. I'm pretty sure it came from Amazon.
I also have a Lifeproof case. They are WELL worth the money. The only reason I don't have mine on is because I have a radio in the barn that I dock my phone on and listen to music, and I can't use it with the LP case on it. I use it multiple times daily, so ... can't do it.
Those Speck cases Jinx posted are good. I like 'em, but don't have one. Might be my next case purchase. If you can't tell, I'm quite mad about cases ... I have 6 of them :p One thing I would advise you against if you get your phones dirty too often are Otter Boxes. Yea, they protect your phone from drops, but they get NASTY dirty. They aren't waterproof either. If you are constantly in a dusty/dirty environment and want good protection, get a Lifeproof. You CAN get them used, but I would make sure you have the seller water-test it BEFORE you get it, and never get one that is damaged.
You can get those leather-like flip cases from amazon as well. You can also get a wallet, which is what I have! A zebra print wallet that my iPhone slips into. Again, friend got it for me from DEB, but they might have them elsewhere ... here are a few of those flip cases you mentioned - from my favorite case hub! :p Amazon.com: Wallet Dot Leather Case for iPhone... Amazon.com: eForCity Compatible with Apple®... Amazon.com: Pandamimi ULAK Colorful PU Leather...
So my bottom line? Either LifeProof, or get one from Amazon :)