Windows:
Smart FTP:
http://www.smartftp.com :
An excellent FTP package. Has many advanced features and is free for personal or educational use.
FileZilla Open Source FTP / SFTP Client: http://filezilla.sourceforge.net/
resume uploads or downloads, works with firewalls, supports SFTP (Secure FTP) and SSL secured connections, handle queues of files to be uploaded/downloaded, etc.
RS FTP:
www.research-systems.com :
Offers an easy to use Windows FTP Client for a 21 day free trial. Ideal for both beginners and advanced users.
AceFTP:
www.visicommedia.com :
A free, but not so beginner-friendly FTP client for Windows. Requires user registration.
Core FTP Lite:
www.coreftp.com/ :
supports ploading/downloading/deletion of directories (folders) and files, browser integration, SFTP (or secure FTP), SSL/TLS, handling of file permissions, transfer bandwidth control, etc.
FTP Navigator:
http://www.internet-soft.com :
An FTP client that is good for both beginners and advanced users.
WS_FTP:
www.ipswitch.com :
Offers both a commercial FTP program, and one that is free for personal use. Extremely reliable.
FTP Surfer:
http://www.whispertech.com/surfer/ :
A completely free FTP program with a good user interface that is very fast and easy to use.
FTP Editor:
http://www.ftpeditor.com :
Allows direct editing of files on an FTP server. Great for web designers, programmers, and consultants.
MacOS
Transmit:
http://www.panic.com/transmit :
A feature-rich FTP client for MacOS. Will run on almost all Macs, even some non-PPCs.
Fetch:
http://fetchsoftworks.com :
The most popular Mac FTP client. Free 15-day trial available, and free for educational or charitable use.
Fugu - Mac OS X SFTP / SCP / SSH FrontEnd:
http://rsug.itd.umich.edu/software/fugu/
Fugu is a free open source frontend for SFTP (Secure FTP), SCP and SSH. It is released under a BSD license, and supports Mac OS X.
Interarchy:
http://www.stairways.com :
A more advanced FTP client. No demos or trials available.
Captain FTP:
http://captainftp.xdsnet.de/ftp/description.htm :
A great FTP client exclusively for Mac OS X.
Cyberduck
http://cyberduck.ch/
Cyberduck is an open source FTP and SFTP browser for Mac OS X. It supports drag and drop, resuming of uploads and downloads, synchronisation of files on a local computer with a server, uploading and downloading of folders, etc. It is licensed under the GNU GPL.
PalmOS
LFTP:
http://lthaler.free.fr/lftp.htm :
A nifty PalmOS FTP client. The program is command-line based, so beginners may have some trouble. There is no graphical interface as of yet, but the software is still very handy and 100% free. It is a great tool for professionals. Requires a PalmOS organizer with an Internet connection.