Most of us have a scroll wheel in our mouse that clicks at regular intervals. While this works fine for many, if you want something that moves a bit more freely, it's actually quite simple to remove the click.
As Instructables user Crash2108 shows us, there are two little springs inside your mouse that govern the wheel's movement. Removing one of these (specifically the left one in the picture above, but your mouse may vary) will result in free-scrolling action. Check out the link below for detailed instructions on the teardown.
How To Make A Mousewheel Scroll Smoothly [Instructables]