I've long liked the idea of multiple arms and hands. After some mental experimentation, I've settled on four arms, mainly because I can keep track of four mentally, while six start to tax this poor old brain and also make it tricky to attach to an otherwise human torso.
However, I'm totally up for greater numbers of other types of manipulative limbs. Doctor Octopus tentacles are A-OK. A rapidly serially switched set of minimanipulators would be cool too - only two or three might be in motion at any one time, but having a dozen which could be used as high-speed clamps, grippers, and general picker-uppers would be very cool. Additionally, I could get comfortable with controlling a small factory of moving parts that each did its own thing.
The
furry avatar of mine I've mentioned before is not only interesting because he's quadrupedal and not even partially humanoid (I never really liked the centaur shape - spines shouldn't bend like that), but because he's got four arms for picking stuff up, hanging from the ceiling, and generally being awesome. He could probably even drive a car, although there's simply no way he's going to be able to disguise himeself as anthropoid, even standing on his hind legs - he's simply got limbs in the wrong places.
That said, when thinking about which character I'd like to play in a fantasy or sci-fi setting, I'm much more likely to pick the one with extra arms. Whether that be General Grievous or the friendly local insectoid race, I'm all about being able to play two guitars at once or just scrape dinner from a plate into a bin with a manually lifted lid while on the phone.
Finding clothes aside, it'd just be generally more interesting all around to have extra arms.