Everyone is a little different, but here are my personal rules of thumb for dressing right for cold temperature road rides (mtn bike I tend to not need to bundle up so much since wind isn't a factor and I'm redlining the whole time):
50s: usually a base layer top with jersey, arm warmers; bib shorts and knee warmers (if in the high 50s I skip the knee warmers)
40s: base layer, arm warmers, long sleeved jersey and wind vest; bib shorts and leg warmers. Maybe a beanie to keep my head warm. Light gloves
30s: base layer, arm warmers, second long sleeved layer under a jersey, thermal vest; bib tights. Beanie on head, shoe covers on feet. Heavy gloves
20s: same as above, but with full thermal shoe "booties", second layer usually a thermal shirt. I double the glove layers: one thin, one heavy duty
I've been out in 16/17 degrees before, but it very rarely gets that cold here in NC, and that's about my limit anyway.
As for brands, most of my stuff is through whatever company is doing the custom order for my team (usually Voler--good solid stuff, not terribly expensive, but also kind of boring), but you can find good deals on winter gear at www.realcyclist.com.
Pearl Izumi makes great gloves and shoe covers/booties.