I suppose that depends on what you're putting in it, and what you want out of it. ;]
I used a Thermaltake Shark for my last build - decent aluminum case, large enough for pretty much anything you'd event want or need, and won't break the bank. I built a machine for a friend of mine using a Kandalf - beautiful, sturdy tower, enough air for casual gaming, but as you would expect from a steel case, the damn thing is heavy!
I have an Antec Nine Hundred sitting in the corner of my office right now, eager to be filled after my next paycheck - for all the lame hype surrounding it, I couldn't overlook the air cooling potential, easy-to-access USB/audio on the top, and lack of a door (I'm looking at building a 5.25" bay-mounted LCD panel, as a way to introduce myself to modding). It isn't as roomy as the Shark, but it's still enough to house an ATX board.
What do your specs look like, by chance?