I don't think I'm doing anything this year... if I am, it's getting late for anything really creative.
My two favorite costumes I've done in the past were:
1. Senior year of high school - Hell's Grannies from Monty Python. I had to improvise on a few things that I didn't have at home. I wore an old lady dress, hair kerchief, little white gloves, and my brother's army jacket with "HELL'S GRANNIES" on the back in white medical tape, with assorted rock buttons all over the front, a cute little old lady handbag, and a fake cigarette dangling out of my mouth all night. Old lady makeup and hair, of course. My best friend was similarly attired.
2. Senior year of college - Keith Richards. It was very much cheating, as the semester before I had taken a stage makeup class, and along with the textbook, we had to purchase a professional makeup kit. My hair was pretty short at the time, and with the makeup kit, it was really an easier costume than you'd think. I messed up my hair and just left it sticking out all over. With the kit, I then did a bump on the bridge of my nose, salt and pepper hair, creases and lines around my face, general unhealthy pallor, dark purple circles under my eyes, and with a stippling sponge, some pretty cool razor stubble. One single small hoop earring in my ear, unlit cigarette hanging out of my mouth, black jeans, black boots, a white button up shirt, a black suit jacket (the outfit: think how he's dressed in the video for "Start me up"), a bottle of booze, and my roommate's guitar slung across my back. The theme of the party was "Come as your favorite British rock stars", and frankly, I'm not pretty enough to have gone as Nick Rhodes (that one's for Summer Smile). Plus, more evidence of cheating - in the stage makeup class the year before, one of our projects was "Make yourself up like someone famous", and provide a picture to compare. So I had already done the Keith makeup for the grade - got an A+, but grossed my professor the hell out.
I wish I had pictures of both, but I'm pretty proud of how they turned out on both occassions.