If you use FireFox, you can choose the default dowload location which I always put on my largest drive and name it My Downloads. Every once in a while, I list the contents by size and delete the big ones. If it is an important file (like Eudora and so on), I save it a level deeper.

I dl loads of stuff (from trusted sites) and mostly wait a couple days before installing and i usually decide that I don't need it and delete the file.

FF has a pop-up that tells you when your dl has completed and has a button to open it immediately, which is cool but then I end up with a lot of installed stuff I never use, sigh!