Instead of replacing light fixtures, fix them up! -- Tack a scarf or square of neat fabric to the ceiling over the light fixture. The fabric hangs far enough down that it won't heat up or scorch, and the pretty colored light shines through below.
Tutorial: 'Chandelier' Light cover - Great for rentals, apts, dorm rooms, etc
My house is FULL of these awful lights.
Cover fluorescent lights with lattice covers. 42 Ingeniously Easy Ways To Hide The Ugly Stuff In Your Home
8 ways to cover ugly light fixtures. I like the parasol idea.
Wire fruit bowl used to makeover "boob" light fixtures - the existing end cap holds it in place.
Genius idea for disguising ugly light fixtures
Search Replace light cover on ceiling fan.