I've been using a XinTD C8 flashlight in a $2 rubber U shaped flashlight holder (holds 1" diameter light which is the common diameter of C8 form factor lights.). Probably about 700 lumens. On the helmet I have 5" barrel flashlight, about 400 lumens. Mine is a Shiningbeam S-mini, but the Convoy S2 is an excellent inexpensive light.

I have been using the same lights and mounts for 10K miles over several years. I had other mounts before these, but I am so happy with these I stopped looking. Total investment for lights, batteries, charger, mounts about $100. I'm with you on the convenience of carrying a spare battery.

I do like my Cygolite Metro 550 for daylight flashing light, but it won't last the 1.75 hours on highest steady beam when I decide to bike home at night.

Here are photos of the two holders:

http://www.outdoor-oprema.com/image/...03-600x600.jpg

http://img.dxcdn.com/productimages/sku_12000_1.jpg