For people having a niche that isn't specific, but generel (or adult in my case) there is a cool site made named Buzzom.Com.

All you have to do is giving in your username, allowing access to the site (it's completely safe, doesn't send tweets and add hidden users) and than you can easily flush (remove people not following you back), grow (add new twitterers) and reciprocate (following back people that are following you).

Every Twitter user should check it out, the site is amazing IMHO and also this one is a website I'm using daily