Yeah, even backing up everything once a month will save you a ton of headaches. Really once a week for home users is good practice.

http://www.newegg.com/Product/Produc...82E16822154611

Something like this is perfect for backing up since it will hold most of your stuff outside of videos or other extrememly large files/folders (anything in excess of 100 gigs). An external drive like this at 160 gig is big enough to back up 3-4 computers really if you only backup the stuff you really need off each one.