I was playing around with MongoDB and node ..needed to add PATH to get mongo commands from anywhere in the shell.
Super easy once you know it.
Open shell and type:
open .profile ( this will open the shell with textmate )
and then update the path :
export PATH=/opt/local/bin:/opt/local/sbin:$PATH export PATH=/Developer/mongodb-osx-x86_64-2.4.6/bin:$PATH
Restart shell and it should work.