Well, if you are running Windows 7 you can use the built in utility to create a disk image. I did this and found it to work quite well so go with this if you are running 7. If you are not running Windows 7, then there is a lot of software from free stuff to paid. Comes down to preference and features. Outside of Windows 7, I have also used Acronis True Image which I thought worked well and does a lot more than I need but I have a handful of PCs and laptops in my home network so I can set up a backup on several machines over the network and save the image to my server.
For a simple solution, you can check out software like WinImage http://www.winimage.com/winimage.htm or Clonezilla http://clonezilla.org/.