SmartFTP FTP software has good double–sided secure transfers through SSL/TLS connections and verifications through basic filtering, XCRC, XMD5 and XSHA. It even supports client certs and Clear Command Channel (CCC).
SmartSoft has created an excellent FTP program that is free for non-commercial use or only $36.95 for a license. They offer modules in over 15 localized versions and host non–English language forums. It is available in 32–bit and 64–bit PC versions.
The only major weakness of this program is that it does not support the SSH security protocol for UNIX type systems, if you need this capacity or a Mac FTP client, see CuteFTP.