There are three ways to go with a dive watch.
Simple and traditional - An analog watch with a locking crown, watertight to at least 100M and preferably 200M, a one way ratcheting elapsed time bezel, large easy to see glow in the dark hands, and a sweep second hand. Both Citizen and Seiko sell very good dive watches that meet these criteria for around $150-$200 and you can cut the price in half on line.
Simple but digital - A cheap but reliable water resitant watch like a Casio G shock or Timex Ironman. Watertight to 100 meters, stopwatch function backlighting, and most importantly buttons that can be pushed underwater without leaking. Cost is $35-$50 at Wal-mart.
Complex with great geek appeal - Any of the variety of watches with integrated dive computers, depth meters, bottom timers, etc. Cost is anywhere from $250 to $1000.
I have a passion for simple and traditional and wear a very nice Citizen promaster most of the time, but a Casio G-shock is very hard to beat in terms of bang for the buck and the cost is low enough that if it dies or gets lost, you are not going to whine about it.