There’s a great article CLI Magic: Searching with find over at linux.com which has examples of using the command line’s “find” utility.

Examples include:

By size:
find /home -name "*.txt" -size 100k
find /home -name "*.txt" -size +100k
find /home -name "*.txt" -size -100k

By user:
find /home -name "*.txt" -size -100k -user paul
find /home -name "*.txt" -size -100k -not -user paul

By Permission:
find /home -perm -o=r
find /home -perm -o=rw
find /home -perm ugo=r,u=w