I attend a lot of conventions, most of the time as a member of the paying public, but sometimes I get invited to be a guest or take up a vendor table to display my art. At these cons, I get a lot of requests for convention sketches, which I'm only too happy to oblige.
A convention sketch is a mini commission, the client chooses a favorite character or scene, and returns later in the day or weekend to pick up their drawing. More than half of the time, it's something familiar, a standard hero or horror film character, like this scene from The Crow.

Other times, the requests can be... different. At horror conventions, I get a lot of mashup requests, such as "Make Hellboy fight a Predator", or "Show Freddy jabbing Michael Myers in the butt." At comic cons, the requests tend to be of the gender bending variety, like "I want a female Superman. Not Supergirl, but a female version of the normal Superman. With huge boobs."
Sometimes, I get requests for musicians, which seems a little out of place at horror or comic cons, but there's a fan for every celebrity, so who am I to question? I received this request, and since it was stippled (and time-consuming) rather than a pencil sketch, I had to send it to the fan after the con.

What character or celebrity would you request? One of the rewards of doing this type of art is finding out what people love, and sometimes, I'm led to discover and appreciate the work and life of someone new to me.