Twitter – What’s the best way to search for old tweets

Remy Sharp wrote a website application that will search your, or someone else's tweets without the limitations Twitter imposes so you can search far further back in time. It's at http://snapbird.org/.

the regular search.twitter.com limit used to arround 1500 a day

And

The search api used to be restricted to a limit of 150 tweets. And a year ago it was also restricted This limit is currently around 1.5 weeks but is dynamic and subject to shrink as the number of tweets per day continues to grow.