I am a huge fan of the website AlternativeTo.net. I have been using it since they were in their infancy, I submitted several product reviews and filled in a few blanks in my time on the site. It’s a very useful site for tech geeks like myself, who might be looking for a program that is similar to something else, but might be more affordable, or have a different feature set. If you want something similar to Norton Ghost, it might suggest Clonezilla, or if you want DropBox, you might want to check out SugarSync or SkyDrive.
AlternativeTo covers all of the major platforms, from Windows, to Mac OSX, to Android, iOS, and even WebOS… you can find great suggestions if you’re looking for an app similar to another, because one doesn’t quite suit your needs. I can suggest the website enough, it’s all built up with user feedback, and I really hope it’s around for years to come.