Bill O’Brien, writing for PC World, has a pretty detailed review on 3 NAS (plus one DAS) device for SMB backups.  NAS devices are network attached storage, basically a hard drive array with a tiny operating system and a network card.  The draw is that they can be configured and then added to your network and used from anyplace that has network access.  This makes them great for file storage and the first stage of backups.  DAS is direct attached storage, basically a USB drive.

NAS and DAS make great places to save files or do your initial backup.  I would be remiss if I did not further recommend actually backing up offsite.  Theft, fire etc at your office would make your NAS kindof useless.