Here are 2 of my favorites twitter unfollow tools. I just use the free versions, which have unfollow limits. When I want to unfollow more than their limit I use another tool listed below. Usually I don't unfollow more than fifty people a day. And only unfollow people about once a week.
Crowdfire (Formerly JustUnfollow) is my favorite, I like it because it displays information about the person twitter account, which helps me decide whether to unfollow or keep following that person. It shows you how many tweets, following, and followers that person has. And if you click their link it displays their twitter profile. You can also click on their @twittername to go to their twitter page and read more tweets if you like. There is a fifty daily unfollow limit for the free version.
Friend or Follow has been around for years, it's the first unfollow tool I used. No unfollow limit. Their main page displays pictures of people who aren't following you. When you click on their picture, it will open their twitter profile in a new window. You can then unfollow them on twitter. You can also use this tool to see who's not following you back on Pinterest and Tumblr.