Don't necessarily wait until after Christmas to buy lights. Yes, the prices will be lower, but so will the inventory. In the past, Lowes has marked down their lights and other decorations 50% off on Dec. 1 or around there somewhere. A few years back I bought over 100 light sets that way. A few weeks later, when it went to 75% off, all that was left were yellow and purple strings.
It varies year to year, based on their inventory, sales, and I think even partially the weather. Keep an eye on the forums, because someone will usually post when the sales starts, and what is a good deal.
Also, if you are going the LED string route (not smart or dumb strings), do a bit a research on them. Some do not dim well, if at all. You also will pay more for LEDs, and in the long run that will save you money in power. However, I have heard that some of them are not as waterproof as they should be, so after a few seasons, the leads connecting the bulbs to the power corrode and they no longer work. So you might be better off paying a little more for quaility in the long run. Incandesent lights are all pretty much the same from what I have noticed (though the colors can be drastically different between manufacturers)