You need lightweight waterproof over trousers too. By the way most ordinary jackets can be made very water resistant by the application of waterproof sprays etc. Grangers make the best water repellent sprays. These are essential for cheaper water proof jackets which loose their water proofness after a while.
A good idea is to buy a big metal can of fabsil not the aerosol, which you can find in most camping shops as this works out cheaper in the long run than the aerosol sprays and paint it on every few weeks. A big can should last for a couple of years. Thompson's waterseal which is sold a DIY shops like Robert Dyas is bascially the same thing as Fabsil and can also be used to waterproof clothing.