Dictionary definitions of a word:
define:word
Faster than going to dictionary.com, though not as complete
Search for a string in the URL:
inurl:string
Handy for when you remember part of the url
Specify the file type:
filetype:pdf(or whatever)
Handy when you want to exclude pdfs (ie -filetype:pdf), or when you’re trying to find something in particular and need to narrow down the search
Metric conversions: rtfm
Great for converting metric and imperial, or basic calculations when you can’t find your calculator and the OS’ calc doesn’t cut it