Smart FTP - an impressive free piece of software with plenty of features (including the ability to view files like .htaccess which most other rivals can't see in their standard configurations).
FileZilla - First I used WS_FTP and thought it was great; then I used CuteFTP and thought it was great; now I use FileZilla, which is 100% less expensive than either program, and it is great. It doesn't have quite as many features as CuteFTP, but it's faster and more reliable. I'd say give FileZilla a try for basic uploading and downloading, then go to a more feature-rich client if you feel the need.
