When we bought our house in '96, it was 25 years old and all the baseboard heaters were rusty and looked like crap. I painted them all with a paint brush with regular latex paint, and they looked great. For about 5 years. We are now refreshing the house, and decided to go with Neat Heat baseboard covers. They are a bit pricey, but they look great and I will never have to paint them again. They just go on right over the original covers. I got them at Home Depot.
http://getneatheat.com/