CLRMame Pro is one of the most useful utilities available to the emulation scene. I started using it about November 2000 and now I swear by it. Once I had it sorted I saved myself about 300MB of hard disk space and was completely surprised just how mucked up my rom files were. For avid emulation fans it's one of those "day to day" programs that you always use.
CLRMame is a set of tools that manages your rom filles. Nearly all emulators use rom files to store their games. What CLRMame does is to check all of the individual rom files against a data file to make sure that they have the right information in them. Data files are available for nearly all arcade emulators and also some console games too.
A word of warning though, because this program moves, adds, deletes and renames files it is best to have a backup of any files that you check because the author of CLRMame and myself take no responsibility for any lost files.