Normally I hate the idea of a token evil character in a group, but for some reason I adore these two and their antics in their respective comics.

I think part of it is that they actually receive occasional comeuppance for their misdeeds and sometimes show a little depth or development. It's aggravating to see the unrepentant asshat get rewarded time and time again for being a smug jerk, but it's funny to see his cruelty backfire in catastrophic ways.

That and they're funny. A lot of people seem to think cruel = funny, but there's more to it than that.

Belkar is from Order of the Stick and Black Mage is from 8-bit Theatre, for the curious.