Below is a list of FTP sites that serve public file downloads. This list is (relatively) actively maintained, as many are sadly shutting down their FTP servers and moving to WWW nowadays.
Address: thrashnet.org
Port: 21
Username: ftp
Password: N/A
Address: mirrorservice.org
Port: 21
Username: anonymous
Password: N/A
Address: ftp.gnu.org
Port: 21
Username: anonymous
Password: N/A
Address: ftp.grandis.nu
Port: 21
Username: ftp
Password: N/A
Max connections per IP: 1
Address: ftp2.grandis.nu
Port: 21
Username: ftp
Password: N/A
Max connections per IP: 1
Address: repo1.macintoshgarden.org
Port: 21
Username: macgarden
Password: publicdl
Max connections per IP: 3
Address: ftp.macintosh.garden
Port: 21
Username: mirror
Password: mirror
Max connections per IP: 3
Address: ftp.scene.org
Port: 21
Username: anonymous
Password: N/A
Address: ftp.osuosl.org
Port: 21
Username: anonymous
Password: N/A
Address: cygwin.osuosl.org
Port: 21
Username: anonymous
Password: N/A
Address: ftp.elf.stuba.sk
Port: 21
Username: anonymous
Password: N/A
Address: ftp.sunet.se
Port: 21
Username: anonymous
Password: N/A
Address: ftpmirror.your.org
Port: 21
Username: anonymous
Password: N/A
Address: space.mit.edu
Port: 21
Username: anonymous
Password: N/A
Address: ftp.ai.mit.edu
Port: 21
Username: anonymous
Password: N/A
Address: ftp.grnet.gr
Port: 21
Username: anonymous
Password: N/A
Address: bitsavers.informatik.uni-stuttgart.de
Port: 21
Username: anonymous
Password: N/A
Address: mirrors.lug.mtu.edu
Port: 21
Username: anonymous
Password: N/A