grep

-i # case insensative match
-v # inverted match (print all lines that do not match)
-c # count the number of match for each file
-l # (letter l) print only the name of the file that match
-L # opposite of lowercase l
-n # display line number
-o # (letter o) show only part that match (handy if you have line that span several screens)
-w word # if you are searching for a word and want to suppress partial matches

grep -rl pattern *