i strongly recommend stayin away from eBay, if your item is defective, there will be problems getting it fixed or replaced. kramer's suggestion of Lumens Factory and Solarforce are great recommendations.
However, if you do want a budget option, i have personally bought
this one and its currently sitting in my G2. It's not a 3 mode as it states but is actually programmable you use the momentary on button, press twice and hold and the light will ramp up, blinks twice at 5% - 50% - 100% and its pretty darn bright too. Only thing is that with this drop in you cannot rapidly press the momentary on for a 'strobe' signalling effect. Oh, and i use this drop in with 3.6v RCR123s (rechargeables) with no problem.
The minimum is VERY low and the max is very respectable too.
There was another i bought but it doesnt seem to be there anymore.