The Silver Searcher is a code searching tool similar to ack, with a focus on speed.
sudo add-apt-repository ppa:pgolm/the-silver-searcher
sudo apt-get update
sudo apt-get install the-silver-searcher
Sadly I get this:
W: Failed to fetch http://ppa.launchpad.net/pgolm/the-silver-searcher/ubuntu/dists/saucy/main/binary-i386/Packages 404 Not Found
If you're running Ubuntu older than 13.10 you have to build it manually.
sudo apt-get install silversearcher-ag