I run a triple combination of lights, respectively.

My main set-up is a NiteRider MiNewt Pro 750. I can get anywhere from 1-3 hours of actual runtime out of it, depending on if I'm using the lowest setting (500) or run into a stretch of road where I feel I need to go with the 750. There is about a 10 minute section I can think of off the top of my head that has no active streetlights and traffic is moving along at 45 MPH.
I have a backup (which is actually my wife's main light) - a NiteRider 650 I bought her. I've gotten decent run times out of it, and it's plenty bright enough for actual riding, not just "being seen." My 11-year-old son has used it for many of our early morning 30-40 milers.

I just recently ordered a Knog Blinder 200L as a permanent back-up to run on longer trips. I'm starting to find myself wanting to try an all-nighter, and will need the three lights for my Vaya. I run two Knog tail lights right now (the second was ordered with my Blinder). I have the older 44 lumen taillight and can say it's very visible; I purchased the 66 lumen to move my 44 to helmet or pannier duty.

All in all, I feel like the cost of running quality lights is worth the investment because I live in a non-bike friendly community and want to be seen and see, not just pretend.