Are you looking for FTP client or FTP server? For client, I recommend FileZilla, for server I use War FTP Daemon 1.6 (you can use a newer one but my FTP server is a Windows 98 Pentium MMX 200MHz...so I stick with the old one to keep it fast).
'Course you can always just use IE (I think FF can do it too, but I'm not sure...) if you don't want another app. I do have FileZilla installed as well, though.