If you need serious light power, HID is the only way to go. Compared with quartz-halogen, HID has far longer bulb life, uses less energy and is much brighter. With a pounding 3300 lumens, this spotlight is ideally suited to search and rescue, boating, professional shooters, security or other high-power applications. It's housed in a tough weather-resistant ABS housing and has a handy shoulder strap for extended use. The built-in rechargeable battery gives about 50 minutes of continuous use and it recharges either from the mains plugpack or a car cigarette lighter socket.
There are hundreds of lights that meet the above qualifications though the "dimable" parameter almost excluded most basic forms of spotlight. I personally think the OP should get a budget P7 LED light.
Have a look at some of the Solarforce P7 lights Dharmaone. Most are under $100. This will get you started.
At the design level, dimming a HID is pretty easy. Once they are struck, HIDS power supplies are usually somewhat constant current supplies as well, so one just needs to change the current to the bulb. That said, the bulbs generally have a sweet spot they like to operate in. Work outside that area and the color changes, life can be impacted, etc.