Ripped from FatWallet:

Again this year, looks like Home Depot is giving a $3 discount on any new LED xmas light string purchased if you bring in an old (used or broken) set of incandescant xmas lights to recycle. Dates 11-4-10 to 11-14-10.
In-store only (dang no FW cash)

Limit 5 per customer.

Excellent time to clean out the storage tote of all those tangled light strings!

example: 50 ct. LED dome light set multi color, lower price $5.97 ($2.97 with recycled light set), item 577712
I couldn't find the individual items on their website, and online you have to buy them by the case, but here's the item for reference:
50 ct. led lights

I am sure there are several other styles etc. to choose from.

Warning, last year, they sold out of several colors and I had to hit several stores to get what I wanted, so I suggest you go early!