I actually googled "how many atheists does it take to change a lightbulb" because there are lightbulb jokes about everything and I figured there would be atheist ones. Here's the answers from the first page I clicked on -
Two. One to actually change the bulb, and the other to videotape the job so fundamentalists won't claim that god did it.
None. Lightbulbs don't exist.
None. Atheists are already 'bright' enough on their own.
Two. One to screw it in and one to try to convince the theist that, despite what it says in a 2000-year-old storybook, in the real world you actually have to turn the bulb clockwise.
One, but he'll never be able to fill the dark, gaping hole left in the ceiling until he converts.