Fenders are a must, having a wet butt and skunk stripe sucks as do wet feet. I like the Planet Bike fenders, with mudguards, they were a big improvement over the fenders I had before. Get full fenders with mudguards, short fenders or snap ons help, but not enough. I really believe this to be the biggest issue if you are going to be riding in inclement weather.
I also like packing the heads of every bolt with grease (stem bolts, water bottle bolts, all the brake bolts, deraileur bolts etc). If left untreated they'll rust in no time flat (standing water in the heads) and make the bike look junky. Also lube the chain frequently.
I guess washing the bike would be nice too but that's going to happen when it crawls a few degrees above freezing here.
If you have a choice I think disc brakes are better, I'm stuck with rim brakes and some days they really don't work very well. However, if you are missing the tabs or the wheelset isn't disc ready, I wouldn't worry too much, just make sure they are in good condition.
Does anyone have a suggestion for good pads for v-brakes, for riding in rain, sleet, snow, etc? I've been thinking about something like the Kool-Stop multi compound pads http://www.jensonusa.com/store/produ...+Tectonic.aspx but I don't have a local source for them, anyone know if they are good?