Looking for a new iPhone 4 case or maybe just any case for your new iPhone 4S? Hopefully this will help. There are plenty of lists out there of the "Top ___ [Rugged/Slim/Pretty] iPhone Cases," this won't be that... but it will give you a good overview of the different case manufacturers and places to start your search. I'll also be highlighting some of the outliers that I've found that are worth looking at(if for no other reason than their oddity).
To start out, let's get the list of big players out of the way.
Otterbox: Their Defender series has been the standard for rugged iPhone protection. Their latest offering for the 4/4S does a good job at trimming some of the fat while remaining very sturdy. They also have a few color options including a Realtree camo version.
Marware: Marware doesn't really stand out in any major areas, but they do have a pretty standard selection of different case types and a few outliers. The glow in the dark Double Take Nocturnal is interesting, and the SportShell Convertible offers the choice of flat back, belt clip, or arm band setups.
As for good places to look, I've found two places you might not have thought of looking at for an iPhone case.
Amazon: I know it sounds obvious, but seriously look! Along with the huge selection of having every brand included in the search, there are a ton of knock off/ "cheap china crap" that could be exactly what you're looking for! In fact while looking for a belt clip for the iPhone 4, I found models that were just belt clips that were as cheap as $0.58!
Etsy: You won't find a huge variety in form factor, it's pretty much either skin or stitched slip case, but you will find a huge amount of interesting designs. If fashion is your thing... Etsy is the place to go!
Okay now, I know for a fact that wasn't a comprehensive list... but it's a good starting point... now on to the wierd and wonderful!
I first saw the LifeProof Gen 2 in a swimming pool. The effects guy operating a pirahna puppet just grabbed his iPhone and started using it in the pool without a care in the world. So yeah, this guy is waterproof, not just water resistant, and it's much thinner than any "rugged" case I've ever seen.
Etsy is home to one of the most bad-ass looking cases out there. Called simply Rugged iPhone 4 and 4S Case, this bad boy either belongs in a museum or on the set of some futuristic cop show. And the pleasure of sticking this thing in your jeans pocket can be yours for only $99.97!
This case makes me laugh just thinking about it, but it does make a certain amount of sense. The Shark Eye Rugged iPhone 4 Case has a retractable sliding protector that slides over the screen. It's best to just watch the video to see it in action.
And now we come to what appears to be the BMW of the iPhone case world. Element Case makes cases for all of the iDevices except the iPod Touches. Most of their cases feature slim designs with mechanical fasteners(allen bolts) and excellent good looks. My favorite is the Vapor 4 Case in Black/Blood Red. But if you want to spend the big bucks and show your love for deniable military operations, check out the Vapor Pro Black Ops iPhone Case for a cool $149.99.