1. The Browser, "who reads for no particular purpose other than to find something interesting with which to engage."
2. The User, "who is looking for specific information and uses hypertext to find that information."
3. The Co-Author, is a "collaborator who deliberately insert [his/her] own writings in response to a piece of electronic text." (Think Blogs, discussion lists, and Wikis).
4. A combination of one or more

Source:
Patterson, Nancy G. "Hypertext and the Changing Roles of Readers." The English Journal. November 2000. 74+