Your in-house IT or regular source of IT support should be helping you make this choice.
Are the laptops periodically back in the main office? If so, you can take an image with Ghost or other drive cloning software. If the laptops are distributed to remote users, you will have to rely on the users to make the backups. (Your IT can most likely come up with a reliable method for users to back up their own laptops.)
My personal choice is to take a full image of my hard drive every month, with incremental backups taken at least weekly, more often if necessary.
I've listed some commercial backup and imaging software below. All are effective and reasonably economical, but require different approaches to implement.
Acronis TrueImage - http://www.acronis.com/
Symantec Ghost - http://www.symantec.com/themes/ghost/index.jsp
Winzip - http://www.winzip.com/index.htm
WinRar - http://www.rarlab.com/
There are also Open Source backup and imaging solutions, but I'm not familiar enough with them to make recommendations.