OS X Terminal not recognizing any commands
To reset your path, remove the line that sets the path from your ~/.bash_profile or equivalent, then reopen your Terminal.

Edit it with /usr/bin/nano, or /usr/bin/open, or TextMate, or any other text editor. It's not that no command can be reached, but that the PATH doesn't include these binaries—they can still be manually opened by providing the path or using cd to the directory.