Most of the time I wear a Fladen one piece suit. With a light fleece under it and the hood up, a decent pair of gloves on, wellies with warm woolly socks and a Save Phace mask available from RIBnet, this can and has kept me toasty warm even in air temps a couple of degrees above freezing, and the wind chill sitting at 30kt for a while is pretty high
Downside is that it's so well insulated you'll cook inside a Fladen when doing any exercise or when the air temp gets much above about 10-15 deg C - I usually launch and then put the suit on after I have been out for a few minutes and I don't usually bother with the Phace unless it's raining - near freezing rain hurts.
If it's reasonably warm, I just wear a decent waterproof jacket and a lightweight pair of oilskin trousers (the sort you can roll up into something about the size of your fist to stuff in a rucksack) over wellies which keeps you fairly dry when there are dolphins jumping in front of the boat and helpfully showering you with seawater about every 30 seconds.