head: a poly-pro type hat that covers the ears (i like the pearl izumi stuff) and maybe a balaclava if for below 35.
jacket: below 45-50 deg i go with a softshell jacket with a thin fleece lining in it and anywhere from a thin under layer to a thick one if its below 20. i like softshells because theyre way cheaper then cycling stuff, theyre super flexible temp wise (esp with pit zips), you can take a spill in them and not rip them apart, and you dont look like a tool wearing them off the bike.
bottoms: i really like the pearl izumi amfib tights (although id go for the bibs next time, no question.) theyre expensive, but theyre worth it. and if its really gross, windy, insanely cold out i like to put a pair of 5.11 cargo pants w/kneepad inserts on, to keep extra warm/dry i almost fucked my knees up last year by pushing too big of gears with not enough insulation, so now i make sure my knees are WARM! watever you do dont get a pair of tights/bibs with a chamois, that way you can wear the shorts you already have and only have to buy one pair.
shoes, socks: i have a few pairs of cycling shoes and honestly my sidis are the warmest most water resistant ones i own. i bought one pair of shoe covers and took them back the next day, not my thing.
socks WOOL no question, a sealskinz over sock below 30deg
gloves: BRING 2 PAIR, nothings worse the riding home in a wet pair of gloves. ow i have a few random pairs and a pair of the big fat peal izumi ones and remember BRING 2 PAIR
also full fenders on the bike will make everything a lot more doable/easy