I also agree with the 2nd post that these (5EX for about 24.95) are great LED upgrades. There are the other terralux ones but I think they are of the older LED technology. I got my 5EX from batteryjunction and the terralux tailclicky thing.
I also got a UCL (the 1.25 one, not the boroglass one for 4.50) from lighthound. At 1st I did'nt think it would make too much of a difference but after reading about it here and then pulling my plastic lens out and holding it up to the light as you shine it on a white background you will see a bit of "tint" or "yellowing" due to the nature of plastics...The UCL is "Clear" and lets about 97-99% of the light through. I read somewhere that the plastic ones will yellow over time and then reduce or change the amount of light that passes it.....
my 2 pennies