Whenever you see or hear the word introvert, it's usually being used to describe someone who spends all his or her time alone, hates being around people and doesn't speak much if he or she somehow does venture out. There's a negative connotation there but that's because of a misunderstanding about what introversion truly is. Sure introverts like being alone, but that's not because they hate other people. It's just that they don't need to be around other people to energize. They are internally motivated. It is their own thoughts that get them going which should be seen as a strength and not a weakness.
There are many jobs that require self motivation, and who is better suited for them than introverts? Take for example, a chemist, who usually works alone in a laboratory, coming up with new knowledge about chemicals to improve the way we live, or a writer, who is always thinking of new stories to tell. There are a lot of other great jobs for introverts. A caution thoughmost of them require at least a little interaction with others, for example occasional collaboration with co-workers or with clients. For the most part, though, you will spend a lot of time working on your own.