Remove empty lines from a file on Linux using command line

This one is especially useful when searching through Glassfish's log files.
There are many ways you can remove empty lines from a file:

• awk 'NF' file
• sed '/^$/d' file
• grep "^$" -v file
• grep . file
• egrep "^[[:space:]]?$" -v file
• perl -n -e 'print unless /^\s*$/' file

And I'm sure there are many more. :)