If you want to have a Mac that's as free from garbage and stray files as you can get, I recommend giving CleanApp a try. The app runs a background process that keeps track of everything an app dumps on your system when you're installing it. When it's time to remove said app, this ensures that CleanApp takes everything off your system that shouldn't be there.
The full version of CleanApp costs $US5 ($7). While there are free apps that are similarly strong at helping you catch errant files that an application has dropped onto your system, I think CleanApp's price isn't so bad given the app's thoroughness.
That said, I recommend giving it a try before you buy. In fact, it's really the only way you'll be able to use the app to its fullest, since it won't have been around to scan apps you've already installed on your system. If you find the whole "background process" bit annoying, I suppose you can always use something like AppCleaner to make sure that CleanApp is completely removed from your Mac when you uninstall it.