It’s possible to force a backup to the OS X Time Machine facility if you have its icon visible in your toolbar, but I find that I really have enough stuff up there so try and keep it down to things I regularly use. It’s also possible to force a backup through Time Machine’s System Preferences pane, but that’s mildly annoying.
I just discovered by accident that right- (or ctrl-) clicking the time machine’s drive in Finder (but weirdly not on the desktop) brings up an extra ‘Backup Now’ option in the context menu.