Well, I thought long and hard....
Hah, no. I always use my first name, and aside from really huge sites, it's always available. I was actually shocked it was available on here, because this is no doubt the biggest site I've joined. Anyway, I completely gave up on creating a good username because I'm terrible at them.
The last one I made was "Stand in Girl" four or so years ago on fanfiction.net (I'm still that, by the way--and yes that was a shameless plug). I came up with that one because I was playing that game where you switch around the words in band names to the opposite and the other person tries to guess them. I was a big fan of Fall Out Boy (I know, I know), and the opposite was Stand In Girl... *cringes* I'd change it on ff.net, but I have a lot of people following me and don't want to lose them. My e-mail starts with Kelseyohsnap, which I get teased for all the time, though I'm not as embarrassed by that one.
So, yes. I dropped everything else and just kept my name. I consider myself a clever girl, but damn if I can't come up with usernames.