Here are some nifty modifiers to type to refine your searches and get the best results using Google search engine.
[" "] Exact Phrase
What it does: searches for an exact phrase
What to type: "one sncall step for man"
What you'll get: results that include the exact phrase "one small step for man"
[-] Excluded Words
What it does: excludes search results with a particular word or pnrase
What to type: bass -fishing
What you'll get: resu Its about bass that are not related to fishlne
[~] Similar Words
What it does: searches for a word and all its synonyms
What to type: ~mobile phone
What you'll get: results with the word "phone," as well as "cell," "cellular," "Wireless," etc.
[OR] Multiple Words
What it does: searches for webpages that include either word
What to type: vacation London OR Paris
What you'll get: results with the word "vacation" and either "London" or "Paris"
[...] Numerical Ranges
What it does: searches for a range at numbers
What to type: Willie Mays 1950 ... 1960
What you'll get: results about Willie Mays during this time period
[define:] Find Meanings
What it does: defines a word or phrase
What to type: deflne:plethora
What you'll get: links to definitions Of the word "plethora"
[site:] Site Specific
What it does: searches only particular websites
What to type: global warming Site:edu
What you'll get: references to "global warming" found on ".edu" websites
[link:] Linked Pages
What it does: searches for webpages that link to a particular website
What to type: Iink:www.umich.edu
What you'll get: websites that link to the University of Michigan website
[1+1] Math Answers
What it does: basic calculator functions
What to type: 4+7, 30% of 55, 20^2, sqrt(4), etc
What you'll get: the answer
[cm in foot] Conversions
What it does: converts units of measure
What to type: cm in foot, 28C in F, $ In pound, days in fortnight, miles in league, mph in speed of light, etc.
What you'll get: the converted answer
adapted from : http://www.google.com/librariancenter/downloads/Tips_Tricks_85x11.pdf