I'm pleased with how my costume turned out:
(If it isn't obvious, I was Dr. Henry Killinger from The Venture Bros.)
I found the mask at the Circuit City Halloween store. I cut off the bottom half and painted it to more closely match the mask. I grabbed the logo from the t-shirt order page online, converted it to a vector then made some stickers for the shirt and Magic Murder Bag. I got the shackles at a Halloween store but they didn't open so I had to cut them and then glue them back together to attach them to the bag. I got the shoes at Wal-Mart (first time I've been there in a while). Slippers would have been more authentic, but they also would have fallen off more often.
I would have preferred a better mad scientist lab coat, but those are a little harder to come by. The stethoscope was a little constricting, but not nearly as bothersome as the mask. I think the mask was reasonably comfortable for a mask, but it was quite a relief when I finally gave up and took it off.