The list below is grouped by general type of role.
An illustrated typology: The Netizens Guide To FlameWarriors
See: A taxonomy of roles: [Social Roles in Electronic Communities] quote:
"Communities are complex social structures that change and grow over time, as a result of the behavior of their constituent members. This behavior is not random, however. Each individual has a set of social skills, privileges and responsibilities within the community that describes his or her behavior. This behavioral repertoire is called a role." by Scott A. Golder, MIT Media Laboratory, Sociable Media Group
Many of the characters above have done good for the community. When I say "doing good for the community" I mean in the sense that the community is richer for their presence, not that the individual effects of their presence are identifiably good. This is a game of the sum of the whole, not the sum of the parts.