If you have been wanting to add additional search engines to Safari's search field, AcidSearch is your software. This has to be my new favorite piece of software (right behind Quicksilver). To add a new search channel:

1. Go to a website that you would like to add and search for something
2. While on that page, go to AcidSearch and click "Edit Search Channels"
3. Click "New Channel"

AcidSearch automatically adds the correct search syntax to the URL field. Feel free to change the name of the Channel and its location on the list.