I agree with nephilim....http://freshmeat.net
I personally like the CLI but I will try to include GUI apps as well.
* XChat (GUI)
* BitchX (CLI)
* gFTP (GUI)
* NCFTP (CLI)
Network Scanning software
* nmap (CLI) - This is the defacto network scanner IMO. You may find some apps which couple a GUI to it on freshmeat.
Photo Editing software like Photoshop
* errr... $~ ssh.