DeClutter
Twitter can be a very useful tool, particularly once you've built up a decent-sized network of people with interests common to your own. The twitter timeline is often compared to being in a pub filled exclusively with your friends, and being able to hear all of the conversations going on at once.
However, just as you have that friend who occasionally likes to go in to excrutiating detail about his collection of porcelain squirrels, there are times when your interests diverge and you'd rather not hear the full details of next weekend's Porcelainathon. And so it is with Twitter.
Once you've started following more than a handful of people, you'll occasionally find your timeline filling up with tweets about things that you're really not that interested in. You'd rather not take the nuclear option and unfollow those involved, as they generally have interesting/useful tweets. But equally you'd rather not have to scroll through 3 pages of automated tweets about foursquare checkins, app downloads and the like.
Enter DeClutter
DeClutter is a javascript bookmarklet which will remove from your timeline any tweets which match a "blacklist" of keywords you've defined.
Below you can enter a series of terms which you want to banish from your timeline (one term per line). After entering them, you can either copy and paste the resulting javascript in to a bookmarklet in your browser, or drag the DeClutter link at the bottom of the page to your browser's bookmarks bar.