Depends on exactly what you are going to be doing and sometimes one belt is not the answer. I have two belts and i'm thinking about getting a third.
Belt 1 - http://www.schiek.com/belts.html
Ignore the bodybuilders, these are the best belts i've found for olympic weightlifting and general training. Broad at the front and the back with a slightly narrower section between the ribs, these belts allow good range of motion for snatch and clean and jerk while being supportive enough for fairly heavy squats and deadlifts. They have a proper buckle thats infinitely adjustable.
The only problem i've had with them is that their sizing chart is a bit out. if you are anywhere near the small end of the suggested sizing buy the smaller sized belt. At 108kg and about a 38" waist I can still wear a "medium". At the top end of PL they aren't really supportive enough and you may find your gut bending the belt out a little.
Beware of cheap imitation belts that look like the schiek belts but have only got a velcro closure, when the velcro wears out a bit they can pop open during a lift - very uncool.
I made pretty much every O lifter in our gym that uses a belt buy one of the Schiek belts and they all love them.
Belt 2 - Want maximum support? Prepared to deal with maximum pain?
Get an Inzer, preferably in pink because if you use one of these long enough you'll be so strong no one will make fun of you and no one steals a pink belt.
maximum PL legal width all the way round, ideal for digging into your ribs and hips leaving bruises and visibly burst blood vessels, also ideal for dieting since doing heavy deads in this belt can cause you to regurgitate your lunch.
On the plus side you get maximum support to brace against and the lever is easy to adjust for length (with a screwdriver) and makes tightening and loosening the belt easy. They also do a prong version and one thats got a ratchet fastening system.
I wear this belt for all my heavy deadlifts and squats and any strongman work like carries.
Downsides - impossible to do olympic lifting in, way too constrictive. Also can get very very painful. Buckle occasionally gets in the way doing strongman cleans.
This leads me to belt 3 which i'm thinking of buying.
It's sort of in between the other two.
4" wide at the back, about 3" at the front and around the hips which means less bruising and less digging into your stomach (=less puke in mouth)
thinner 10mm leather as opposed to 13mm
One of our 105kg lifters wears one of these for his squats and clean and jerks.
If i buy one i'll definitely get it in pink, possibly with rhinestones or sequins across the back