(Taken from the twitter website)
You can make more advanced searches by entering what are called search operators directly into the search box.
(Alternatively, you can use the advanced search form to automatically constuct your query.)
twitter search containing both "twitter" and "search". This is the default operator.
"happy hour" containing the exact phrase "happy hour".
love OR hate containing either "love" or "hate" (or both).
beer –root containing "beer" but not "root".
#haiku containing the hashtag "haiku".
from:alexiskold sent from person "alexiskold".
to:techcrunch sent to person "techcrunch".
@mashable referencing person "mashable".
"happy hour" near:"san francisco" containing the exact phrase "happy hour" and sent near "san francisco".
near:NYC within:15mi sent within 15 miles of "NYC".
superhero since:2009-06-29 containing "superhero" and sent since date "2009-06-29" (year-month-day).
ftw until:2009-06-29 containing "ftw" and sent up to date "2009-06-29".
movie -scary 
containing "movie", but not "scary", and with a positive attitude.
flight 
containing "flight" and with a negative attitude.
traffic ? containing "traffic" and asking a question.
hilarious filter:links containing "hilarious" and linking to URLs.
news source:twitterfeed containing "news" and entered via TwitterFeed