The comedy here should be immediately obvious. I've listed some of my favorites:
Darth EptI wish I were allowed to stretch the rules enough to use "Darth Potent" and "Darth Becile," but I'm not. If you've got a dead-tree dictionary lying around (I don't) I'm sure you can come up with a dozen more. Knock yourself out.
Darth Sider Trading
Update: June 6th... I guess I didn't make myself clear. The pattern is implicit in Vader's and Sidious' names, but not in Lord Maul's nor Lord Tyrannus'. Technically, that means it's not much of a pattern. Still, all of the SUCCESSFUL Sith Lords (ones who get more than one or two movies' worth of exposure) adhere to the pattern. Besides, since many folks are out there saying that something or another could have made Episode II better, I'll weigh in and say that Lords Maul and Tyrannus would have been better named "Darth Fucate" and "Darth Iquity," respectively.
If renaming supporting Sith doesn't keep you busy enough, here's a link to a list of words beginning with "i."