Depends on your needs. If you're talking about you personally at home (or very small business or whatever) then you can do a lot worse than buy one of those plug-in firewire or USB hard disks and backup to that using the Windows backup tool (or some of these plug-in disks come with their own backup software).
Also heard good things about the iomega rev drive, though I haven't tested it myself:
http://www.iomega-europe.com/eu/en/products/rev/rev_family_en.aspx
Pretty simple and pretty damn quick, just what you want for one or two people. At the "home" end of the market, the "right" device is more important than the software because the software tends to come bundled with the device and is more or less guaranteed to work.
If you're talking about a business then we'll have to have a re-think, and talk a lot more about the exact requirements. At work we use Symantec / Veritas netbackup with a robotic tape library thing which is about as complex as doing algebra in a language you can't speak or write, and is priced somewhere in the "If sir has to ask then sir can't afford it" bracket...