Waterproof trousers are the hottest, most uncomfortable things ever. If it's raining that hard, I'm resigned to the fact that my legs are gonna get wet. Make sure your core is warm and dry and legs generally stay fairly warm because they're constantly working
I've got some Gore windstopper running trousers that I really rate. No good if it's properly cold but they're great for this time of year. They block the wind (obviously) and aren't waterproof but dry really quickly. You can layer under them depending on temperature.
What kind of trousers do you guys wear when it's raining a lot? Some waterproofs on top of your tights? Thanks:)