The question is not so much “What kind of geek?” as “How many kinds of geek?” Geekdom is driven by some fairly fundamental characteristics–indifference to whether or not a topic is “mainstream”, obsessive attention to detail, and an inclination to independent thought, among others. It’s not necessarily specific to a particular topic. Geeks often branch out when they find new topics that interest them, or engage in serial geekery, in which they obsess on a subject until they feel they’ve mastered it to their satisfaction, then move on to the next topic.
Here are some (but not necessarily all) of the ways I geek out:
Tech geek–I do software development and testing at work, then do both hardware and software development on my own time.
Anime geek–Not as obsessive as many, but I attend a couple of cons a year, and watch more anime than live-action shows.
SF geek–Fantasy and science fiction fandom runs in the family. Someday, I must find a way to stack books on the ceiling in order to preserve room to move. I have filk CDs.
Comic book geek–I’m sort of abstract about comics geekery. I actually follow very few titles, but I find the tropes of comics interesting, and I know more about superhero characters than a non-geek would readily admit to.
Game geek–This is where I hang my alpha geek hat. I play video games, tabletop RPGs (involved in two different campaigns now, and planning a third), and LARP (live action roleplaying–we dress up in costume and chase each other around the park with foam swords). I’m on the Board of Directors of a non-profit gaming organization and the chairman of the committee that controls the in-game economy (which means I spend a lot of time pricing healing potions and things that go BOOM). Game-related stuff soaks up the bulk of my free time.