For the Magpul forend, I think the InForce WML light is a good option. You can install a short piece of Magpul rail per photos below and then the WML light and its tail switch come right in line with your thumb. It takes a little bit of work to get used to it, but I like this option pretty well. You can see a good review of the Inforce light on the MOE forend here:
https://www.youtube.com/watch?v=Hs49YiGj1qQ
I have the Magpul forend off the gun right now (870 Tactical build) because I'm trying out the Surefire integrated light. It works "OK", but I really don't like the feel so far. For me, the area under your palm is too short for me to get a good grip on the forend (between the yellow lines).
Nice looking furniture.Streamlight makes a light rail which seats between the magazine tube and cap. Not as solid a solution as a dedicated forend light or using the slots in the Magpul forend but it works well enough.
http://www.amazon.com/Streamlight-69906-Strmlght-Shotgun-Rem870/dp/B001G61K74
I like yamadogs suggestions. The best. Seems pretty affordable and user friendly.
Thanks prometheus!
Yamadog-what rail did you use? Did you use the m-lok or the moe? And what length? Thanks again!