I cycle to work almost every day come rain or shine. I wear cycling shorts and vest, a light waterproof fluorescent jacket, a rucksack with a foldout waterproof covering, an underhelmet cap, and I've just invested in some overshoes to protect my shoes and socks. I change into that in the morning, and when I get to work I change into clothes from my rucksack and hang the cycling clothes somewhere to dry if need be. Only when it's absolutely bucketing it down will I consider taking the bus.