Unlike Mat or my son, I can't afford the luxury of an all Castelli or Assos wardrobe, what I do have is a mix of mid range gear like DHB, Pearl Izumi, Altura etc. I also have a couple of pairs of really good winter gloves, plus Castelli toe covers for my shoes.
I find multiple layers work well and have recently bought some On-One merino base layers to try, as an alternative to my ancient Helly Hansen tops, which are still going strong many years after purchase.
Most of my cycling jerseys are s/h from ebay, as you can get some really bad taste patterns for a couple of quid each.
Arm / legs warmers are by DHB and I also some bib type fleece tights that are Italian and seem to work well when worn over 3/4 nicks or ordinary cycle shorts.
Cycle socks are a must, as are a fleece skull cap and a fleece neck warmer or buff.
If it's really cold, then somewhere under that lot will be a windproof gilet.