Here are a few pieces of gear to help you find your way around in the deep blue, or green, brown, or black, as the case may be. When diving, it is important to remember that you need to navigate both horizontally, and vertically. The vertical component is usually taken care of by the dive boat anchor, but emergencies do occur, and you should be prepared.
2016 Update
Nothing much has changed in twenty years. The Tektite strobe is exactly the same, and you can still get good big dive reels, although enclosed models have disappeared. Compasses still point north, and flags are still a bother.
More: Navigational Aids ...