There are a few FTP apps out there.
If you like the command line and the terminal you can always use the ftp command in it, works similar to ftp.exe (The DOS rip off of the UNIX version)
Looking on versiontracker.com I found: VersionTracker.com - FTP]
Fetch - is a very popular FTP client that is used but is shareware FTP Thingy - free and the reviews seem very positive for it.
Also it is possible to simply browse a FTP server by simply entering the ftp address when after selecting Connect to Server... from the Go menu in the Finder
Being in web design, I used Fetch for years, but had problems with it when I went to OS X.
I gave Captain FTP 2.1 a try and loved it so much I paid for it! It was built from scratch to run exclusively on Mac OS X, and they have a slightly older version (v. 1.4) that is also free for students and the like...