I bought LED bulbs to replace some of the halogen spots we had in the Attic. (Well still have as we still own that house even though it's rented out to someone else).

I was doing a "You and your environment" course at the OU at the time. Yes the bulbs are not cheap, and the ones you can get in B&Q don't give out enough light. But even when you buy the larger units on the internet, you save enough energy to recoup the cost relatively quickly.

I did my own post on this a while back, and had a slightly different perspective.