find

To find files with size greater than 1000k:

find / -size +1000k

To find files that have been modified within 2 days:

find / -mtime 2

To find files with size greater than 1000k and list files in 'ls' listing format:

find / -size +1000k -ls

To find files with size greater than 1000k and output extra information about these files:

find / -size +1000k -printf "%r %k\n"

To find files older than a certain file and delete them:

find $PWD -type f ! -cnewer filename -exec rm {} \;