Shooting in the rain can be fun!! No joke. I have had success shooting slow film with long shutter speeds to catch lightning bolts and such. Shoot under awnings, roofs, your car hatchback lid etc. A good tripod and some other simple stuff is all you need. I have spent many an afternoon and evening shooting college, and high school football in the rain with trashbags, ponchos, and umbrellas. Wouldn't recommend that. Rain also provides nice reflection opportunities. Your car windshield offers a lot of potential for interesting reflections in rain drops. Just don't drive while shooting! Puddles are also great fun. Coffee shop windows or other large public places offer nice chances to shoot others battling the elements. Still life has been mentioned. There really is no end to the potential of rainy day photos. Go nuts!!