Twitter Pack Project: Find Twitter-ers by topic, location
The Twitter Pack Project has lists of all shapes and sizes. For example, if you're an Apple nerd, you can find a list of Twitter-ers whose Tweets are more or less related to Apple. Like having a good belly laugh? Visit the laugh pack and become a follower of your favorites. Want to follow fellow Twitter-ers in the same city? Packs exist for San Francisco, Los Angeles, and more; basically every major metropolitan area is included.
If you don't find a pack to suit you, you are encouraged to sign up for the wiki and create your own (the invite key is: project). You can add new lists to existing packs (say, a new geographical location) or create an entirely new pack (for example, packs by birthday dates, and so on).
So what are you waiting for? Get to following.