As it wasn't mentioned yet: pushd / popd

These two commands replace 'cd' and work with a directory stack of different paths.

   $ pushd tmp   # cd to tmp and remember current path /
   /tmp /
   $ pwd
   /tmp
   $ cd /usr   # normal cd to wherever you want...
   $ pwd
   /usr
   $ popd   # pop the stck and get back to the previous path
   /
   $ pwd
   /

Subsequent pushd will stack multiple paths.

It's a built-in of bash and other shells. It works even with Windows' cmd.exe