I like the Kinco insulated hi-vis work gloves down to 18F and are a good value at $15 or so.
http://www.gemplers.com/img/kinco-vi...122060-lrg.jpg
and the skiing lobster claw mittens are good to about 0F, and much more spendy.
http://cdn.outdoorgearlab.com/photos...30_4821_XL.jpg
The loose index finger works very well with rapidfire shifters.

Since I have a dedicated winter bike with 1x gearing, I chose a shift lever that's easy to work with fairly thick mittens. This arrangement has worked for temps pushing -10 F so far. And for Xmas I got a pair of bar mitts, which are really nice.

A grip shifter should have worked for this purpose, but it was aggravating my tennis elbow.

I have had issues with my fingers no matter what gloves I have tried. It seems that I have some issue with circulation. This year I purchased these:

Heated Gloves - Bay Cycle And Sports - Pickering, Ontario, Canada

I use them like a liner inside heavier gloves. I am really happy with them. I have been out in sub freezing temps and my hands have remained comfortable.