IMO a lot depends on your situation, ie distance, speed and destination. If you're commuting a long distance and might not be able to keep a decent pace up (traffic, not just fitness), then more waterproof layers are good. If you've only got a half-hour commute and you can change into civvies then I agree with Rob3rt, less is more – I just wear bib tights, jersey, gloves and maybe a light 'racing style' wind/rain jacket. If you're able to keep up a decent pace without having to stop all the time for traffic lights etc then don't get too overdressed or you'll just get hot and then wet from the inside. YMMV, everyone has different prefs. For instance, I once had to cycle home from work in an absolutely torrential downpour, my commute was only about 20 mins. I ended up leaving my shirt at work and riding home topless (I am a bloke before anyone gets excited). It was 'warmer' having rain on my skin than a soaked shirt.
Sealskinz (or similar) gloves are handy – cold wet hands reduce the fun considerably.If it's really cold you can get those overboot things but I never have, just a pair of 'waterproof' cycling shoes.
One of those buff things can be handy for face/neck in the cold.
Hope that helps.