A few pointers on cases that I personally always look for.
Don't go for those cheap $30 cases as 90% of them suck and you will regret it and most buy a new case when they upgrade because of this. Look for something that is aesthetically pleasing to you. That said, some of the cheaper generic cases suffer from sharp edges and you can cut yourself on them. Another reason to go with quality case makers like Antec and Coolermaster. Ultimately it comes down to the fact that it's your case and you're using it so get something you like. You're the one using this computer and not anyone on these forums.
If possible, look for a case that can use 120mm fans as this will reduce fan noise. Having lots of fans is not better than having less but larger fans cooling wise and it is loud as heck. Also make sure the fan grill holes are large enough for easy airflow but small enough so you don't get fingers and stuff in there. Too many cheap cases have this crappy dotted pattern design to try to make it look nice but it is completely killing the airflow. This goes for the front of the case as well, make sure air can get in or there won't be any air to push out.
I know people rave about removable motherboard trays and they're nice but a roomy case is just as good IMHO. A good case from a reputable manufactorer is usually a roomy case and should have plenty of room inside to work with. Do your homework though and google reviews for whatever case you're looking at.
I personally hate cases with doors that hide the drive bays. I look for a case with an integrated bezel that hides the dvd/cd drives similar to what's on the Antec P-160 which is the case I ultimately decided to get. The tiny fan grill holes are a major pet peeve of mine and I've seen otherwise good cases go in my crap list becase of it. It doesn't cost them any more to cut bigger holes in the fan grill area so I don't know why they insist on making these stupid radial patterns with tiny tiny holes.
http://images10.newegg.com/productimage/11-124-085-08.JPG The link to newegg showing the back of an Enermax case is a classic example of what I'm talking about. The stupid fan grill area has maybe 50% of the area covered up when they could have made opened it up for really good airflow. And the stupid radial pattern does nothing since when was the last time you the back of the case facing towards you during computer usage?