Which FTP client can I use to upload my web pages?

One of the best ftp client available on Windows is the open source Filezilla (http://filezilla.sourceforge.net/).

On Mac Os X you can use Cyberduck or Filezilla

On Linux Gftp or Kftp (included in the KDE network package) are good choices. Since September 2007 Filezilla works on Linux too.