If you're a unix system administrator, rsync is the obvious choice for speedy remote backups. It only sends the differences of files, allowing me to quickly synchronize a directory of important files offsite. I just recently discovered cwRsync, a packaging of rsync and Cygwin.
Super easy install (even gives me ssh tools) with a windows installer, and I was happily rsyncing backup data from the BillBoards server. I then downloaded NirCmd to initiate a VPN connection, and I was rsyncing backup data from our other Windows server. I wish I would have found cwRsync sooner.