Ask experienced local divers what they recommend. A small light that works great in the Caribbean might not be strong enough to pierce through murky local water. Cave divers will typically use very bright HID lights attached to a battery canister that cost $500 - $1,000. For a beginner recreational diver, a good quality dive light can be had for $100 - $150.
Lots of divers in my local area use the Princeton Tec Shockwave LED or the UK eLED (C8 or C4 version). If a stronger light is needed, then the UK Light Cannon is a good choice, but the Light Cannon is more expensive (approaching $200) and its bulb can be fragile as well as pricey to replace. Personally, I like LED lights because the bulb(s) last far longer than any HID, halogen, or xenon bulbs. The batteries in my LED lights seem to last longer, too.
Regardless of what you purchase for a primary dive light, make sure that you get a backup light as well. Once again, ask local divers what they'd recommend. I have an inexpensive Princeton Tec 40 ($15) that I take on every dive with me.
FYI, a headlamp is very useful to have for pre-dive setup and post-dive break down. I keep one in my car glove box that gets used before/after every night dive.
Hope this info helps...