M4Products.com has high quality 12V LEDs that are fully regulated, not polarity dependent and dimmable. They have a variety of sizes. I purchased the Elite series with the bright 5630 LEDs and they produced more light at 1/5 the power.
They also have fluorescent bulb replacements. Since fluorescent bulbs are efficient the LEDs use 1/2 the power but are flicker free. If you lose a ballast then this will be a cheaper alternative as a new ballast will be expensive. It does require you to rewire the fixture to bypass the ballast.