Nimona, by Noelle Stevenson, is a webcomic about arch-villain Lord Ballister Blackheart and his new sidekick, a shapeshifting girl named Nimona who enjoys destroying things. Together, they fight Ballister's “former best friend turned nemesis,” Ambrosius Goldenloin.
It's fun and funny and silly and a bit slashy and has some nice emotional moments too. And it's a nice mix of science fiction and fantasy without worrying too much about how those aspects fit together.
You could start at the beginning by following the above link, or you could first visit my favorite strip, the Christmas special, which is a standalone page outside of the main storyline. And then go back and start from the beginning.
New episodes are posted on Tuesdays and Thursdays. Oh, and the comments sections are also fun to read; the comic has a devoted and entertaining (and slashy) following.