Canister light is the obvious answer if you see yourself getting really serious about diving. Personally I prefer HID, as I feel there has still been quite a lot of growing pains with the LEDs on the market (like too many duds/issues with people who have bought them, lower percentage of owners who have said they have had absolutely no complaints).
However, how much exactly do you have to spend? There is also a route many of us took when collecting money for the 'ultimate' light and building in experience. You can start by getting an excellent back up light and use it as your primary first. After you have enough money to get the primary (canister) you know you want and need, you can retire your first light to be a high end back up.
Photon Torpedo LED at $150 is one highly recommended. Will work adequate as a primary and be great back up:
gulftex
It's handheld but if you are not too tightly wound, in tight spots you leave it clipped to your chest d-ring, and you can hold it with your hand while it's still clipped, so if you need to let go it just dangles.