After getting a Septor LED headlamp, I love it. Best commercial light I own. 6 LEDs with 3 levels of brightness, runs on 3 AAA batteries. I do not buy any LED lights that run on button batteries as the button batteries cost $5 each around here (except for my Microlight), I can get 2 AAA's from the dollar store.

That said, my idea light would:
- Be cheap on the pocket book
- Be reliable.
- Sip power
- Use a long lasting battery like a 9v.
- Have at least 2 brightness levels.
- Switch between 2 white LEDs and one red led (which sips REALLY low power for those emergencies)
- It should use batteries my other gadgets use, like my GPS (which uses 2 AA)

And so, as a person who also makes simple LED lights, this is my current favorite light I have made. I call it the Altoid Light.
2 ultra-bright white LEDs.
Uses a 9v (cost: $1) which lasts a longgggg time.
Very simple circuit, no voltage booster needed.
Plans and pics here: http://www.geocities.com/csroberts/light.htm

I use this light every night for locking up the house. That means I use it about 5 minutes per day. I also use it when repairing things in dark places. My current NiCd rechargable 9v batt lasted about 3 months on a charge.