PuTTY is a free implementation of Telnet and SSH for Win32 and Unix platforms, along with an xterm terminal emulator. It also includes versions of sftp and scp.
FileZilla Client is a fast and reliable cross-platform FTP, FTPS and SFTP client with lots of useful features and an intuitive interface.
FileZilla Server is a reliable FTP server.
curl is a command line tool for transferring files with URL syntax, supporting FTP, FTPS, TFTP, HTTP, HTTPS, SCP, SFTP, TELNET, DICT, FILE and LDAP. curl supports SSL certificates, HTTP POST, HTTP
... [More] PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, kerberos...), file transfer resume, proxy tunneling and a busload of other useful tricks. [Less]
Konqueror is a file manager, web browser and file viewer, which was developed as part of the K Desktop Environment (KDE) by volunteers and runs on most Unix-like operating systems.
SmartFTP allows you to transfer files across the Internet via FTP and SFTP. It offers a modern look and feel and features including SSL/TLS, FXP Support, Multiple connections, Proxy Firewall support, Drag and Drop, caching and more.
LeechCraft is an extensible crossplatform multiprotocol opensource download manager. Currently it supports BitTorrent, HTTP, RSS/Atom feeds, allows you to chat in IRC a bit and a lot more.