While most people think of LED bulbs when they think of energy-efficient lighting, halogen bulbs are actually a close second. Halogen bulbs use less energy than traditional incandescent bulbs and last longer, making them a more cost-effective option in the long run.
One downside of halogen bulbs is that they can get quite hot, so be careful not to touch them after they've been on for awhile. Also, because they contain mercury, you'll need to dispose of them properly when they do eventually burn out.