As a Southern Californian I almost feel silly answering this question on "winter" trail running.
Is there ever winter here?
I'm running ~35 miles a week and right now, 4-5 days a week. I'm fortunate, I've done only one run on pavement in the last 3 months.
I did 9 miles on trail (mostly in the dark) last Thursday night- could've taken my shirt off...
I ran 16 on some very hilly mountain singletrack early Sat. morning- chilly, I started with a light beanie, arm warmers, and lightweight gloves first hour and a half.
Don't know if this really helps your winter question, but here's what I currently like: lets say it's a long run, some in the dark, cool temps (40-50's).
Shoes: Adidas Supernova Riot, my favorite trailrunner so far.
Socks: Injinji; I'm hooked- no more toe rubbing blisters!!!!
Gaiters: Dirty Girl Gaiters; super minimal, breathable, don't even know they're there, great company, low price, fast shipping
I like short running shorts with sewn in briefs for just about all weather. I'll wear spandex leggings under if it's colder.
I like lightweight short sleeve tops and cycling arm warmers (I have some Pearl Izumi) if it's cool. I throw a light vest (non-insulated) over that if it's cold.
I find a lot of cycling apparel is good for running (wind vests, arm warmers, etc.)
Lighting: Petzl Tikka Plus (the one with 4 LED's). I've experimented with putting it on my waist (I think I heard this from Andrew Skurka)- definitely better at lighting the ground without killing your peripheral vision. Usually I just hold it to reduce bounce.
Have fun...I'm loving running these days!!!