Google offers a range of commands that are not widely known. Most are to be found here.
Command Function and example
Site Domain search (dog food site:dogworld.com)
Link Finds who links to a URL (link:dogworld.com)
Allintitle Searches on keyword(s) in titles (Allintitle: dog food)
Allintext Searches for keyword(s) in body text (Allintext: dog food)
Allinurl Searches for keywords in URL (AllinURL:dog food)
Inurl Searches for keyword in URL (InURL:dog)
Define Lists word definitions (Define:canine)
Related Lists sites 'similar' to another (Related:dogworld.com)
Info Lists what information Google has on the site (Info:dogworld.com)
Blog Search is run from a separate page accessed from 'more Google products' page.
Idiots' Guide
The 'Site' command is ideal for testing keywords on your own and competitor sites.
The 'Link' command is ideal for seeing the number and quality of in-bound links to any site. If you have far less than a competitor you have a lot of work to do on gaining more referrals.
The 'Allintext' and 'Allintitle' commands are very useful for testing keywords