Recently a friend of mine asked me about good programs to find duplicate files. She had important files on two different drives and knew she had a significant amount of duplication, but didn't want to lose newer files in either location. Moreover, she wanted to transfer all of her files to a new computer she had just bought.
I knew of one program that worked for me in the past, but did a little research to find several programs that quickly scan drives and let you compare files to know which ones you can delete. Not only do these applications offer a solution to my friend's problem above, you can also free up a significant amount of hard drive space by getting rid of duplicates.
Duplicate File Finder is a free program I've used in the past that finds duplicates quickly--even on large hard drives. This program is especially good for tracking down and deleting duplicate digital photos or album cover art, offering a small viewing window so you can make sure you're deleting the right picture. The interface may seem confusing at first for beginners, but contextual help balloons will quickly acquaint you with the program's various useful features.
Directory Report 28 quickly catalogs large drives offering numerous features for managing file directories. It lets you sort by several different criteria to find which files you need and which are duplicates. This one offers much more than just the ability to find dupes, but it might be the fastest of the bunch for this feature. You can also easily print directories for hands-on comparisons and export to Excel to view in a spreadsheet format. Directory Report 28 costs $25 after a (too brief) 10-day trial, but if you're serious about managing your files, it might be worth the money.
DoubleKiller finds duplicates according to your specified criteria including a file's name, size, date, and content. Though this free program runs slower than Directory Report 28, it performs its function very well. The ability to search for named files within a certain size range makes it especially useful for searching out MP3s of the same name with slightly different file sizes.
If you need to sync up two computers or just want to get rid of duplicates to free up space, try one of these Killer Downloads. As always, if you have a favorite that's not listed here, please let me know in the comments.