I was going to suggest the Gore Phantom as well. Mine's great. I find it pretty waterproof, and it stood up to the rain as well as the supposedly waterproof jackets of others I've been riding with. The sleeves on my ladies version zip off to turn it into a short sleeved vest rather than a gilet. I got mine for about £75 from
Wiggle during one of their regular promotions. It's still not cheap but I've not felt the need so far to buy a waterproof as well as it suits mosts purposes.