For all of Windows 7's niceties, it still doesn't have an appropriately slick built-in backup system like Time Machine. Enter Seagate Replica, which Rob at BoingBoing Gadgets says works perfectly, just like Time Machine.
You plug it in, agree to the Terms of Service and it copies your entire hard drive—then every so often, records changes you make, so if your girlfriend has second or third thoughts about that home video you made together and deletes it to keep it from haunting her future Senate career, you can just zoom back a few hours into the past and retrieve it. Or any other precious file that mysteriously slips into the ether. If your whole system crashes out, it comes with a boot CD that you're not going to want to lose that'll let you restore your entire hard drive. Also, it looks like a hard drive for aliens.
It's $130 for 250GB of backup, or $200 for 500GB. [BoingBoing Gadgets, Seagate]