Facebook and Twitter are becoming ever more useful information sources. If you saw a helpful post or tweet a while ago but can't remember it exactly, Social Searching (or Socialsearching.info) is a quick and easy tool to help you find it.
With the rate that people post tweets and Facebook updates, it's hard to navigate to older posts, and Twitter's search tool only goes two weeks back. The very simple Social Searching site lets you search for all tweets and Facebook updates.
You'll need to first sign in with your Twitter or Facebook account, but the developers promise they don't store any of your information or post anything to your wall.
Twitter searching, I found, works best if you enter the name of the person as well as the keywords you're searching for. Besides helping you find specific tweets, it's also an interesting tool to get a list of all tweets by a particular user on a topic from as far back as possible.