None.
It may be time efficient to make a catch-all image of your HD, but it's not particularly clean.  You never no what little glitches you will be bringing to the freshly formatted HD when you need to restore.  It is also counterproductive to make a drive image of a relatively bare Windows installation with only the appropriate hardware drivers and desktop settings -- this cripples you because new drivers come out all the time and you are stuck updating old legacy software.
The best way to make backups and have complete control over the new virgin HD is still to go through your drive, find out which data files are necessary to you (ie. personal records, financial accounts, word processing documents, digital music, etc) and copy them to a temporary folder before burning them with whatever CDR software you prefer.  If you were well organized to begin with, these files would all have been stored under a common folder such as "My Documents", and given descriptive names and subfolders.  Do not even attempt to backup programs, simply reinstall them from their original CD's to ensure a clean setup.  Then copy your data files back in.
This might be a little more work than a mindless Ghost image, but it is so satisfying to have a fresh Windows installation with only your desired applications and data, free from legacy registry settings, INI tweaks and the like that always stick in the back of your head when diagnosing a software issue.
Modus