It's not memory that is full, it is the hard drive.
#0 - Reboot
#1 - Empty the Trash
#2 - If you have any obvious files of your own you can delete, do that and empty trash.
#3 - Open your web browser(s) and delete their caches or 'temporary internet files'
#4 - Go to
http://www.versiontracker.com and download DeLocalizer. Run it and delete un-needed language resources. That should gain you another GB or so.
Now -- get yourself an external drive and move your bunches of {whatever} to the external. Take the opportunity to install an OS on the external drive and some utilities, so you can boot from the external if you have trouble with your internal.
Make backups. Get SuperDuper.