7. The arrows
Chances are that the first experience you had with a user interface, might have been your first experience with a computer altogether, someone told you that to scroll down the page, you use these arrows strategically positioned that scroll the page. This is officially the worst way to scroll, it's incredibly slow, and you have point your mouse at the tiny buttons each time.

Corollary: Some ui technologies emulate this button (certain flash sites) and instead of making you click it, they scroll when you hover over it. This is an improvement, albeit a small one. Most importantly, you still can't control the rate of scrolling.

6. Dragging the bar
Now you're one step up from clicking on the arrow. You realize it's too slow, so you grab the bar and drag it. This is a very imprecise scrolling method, but a much faster and empowering one. The problem is that you still have to use the mouse button for this, and since scrolling is something you do all day everyday, this is way too much mouse dependency.

5. Clicking the meter
Clicking is an improvement on dragging, so your hand will prefer this. You click the gray area where the bar is absent and it scrolls page-by-page. You also don't have to position the pointer as exactly, just as long as it's somewhere on the long gray bar, much better. Here uis differ, some stop scrolling once the bar reaches the position where you hold your pointer, which is logical, others don't.

4. The arrow keys
What if you didn't have to use the mouse at all? Face it, the keyboard is a much faster control device, and before you had windowing applications with hundreds of pixels to traverse, you didn't need a mouse at all. And it's a much more pleasant control too: I don't know about you, but I find pressing a key much smoother than clicking the mouse button. Maybe you have a fantastic mouse. So yes, you can use the arrow keys. But the rate of scrolling is the same as that of the arrow buttons, so you trade in control for ergonomics.

3. The mouse wheel

Back to the mouse, hah, bet you didn't see that coming! Oddly enough, you might say, the mouse wheel didn't enter the mainstream until a few years ago. It's true, if you go to a museum that has computers from 10 years back, the mice don't have wheels. The mouse wheel is a big improvement, because it doesn't divert your mouse movement to that damn scroll bar on the right side. When you click around, you can just keep your pointer exactly where it is and scroll with the wheel, it's fantastic. But again, the scroll rate is limiting (but it's more than the arrow buttons). If you need to scroll a big amount, the mouse wheel is out.

2. Good ole spacebar

Who'd a thought, after all these years, eh? The spacebar is positioned optimally. If you're right handed, your right hand will cycle between the keyboard and the mouse, but the left hand will be on the keyboard. And vice versa. The spacebar is right underneath your thumb, it's the quickest way to scroll. And you scroll page-by-page, which is efficient too. But it only scrolls down.

1. PageUp/PageDown
This is just like the linux programs more and less. The former only scrolls down, the latter scrolls up *and* down. The location of these keys isn't as good as spacebar, but they are still nearby for the right hand (even better if you're left handed and operate the mouse with it). The keys are at the end of a row, so it's easy to find them without looking. They (obviously) scroll page-by-page and so you have full flexibility. If you're only reading something and you keep scrolling down, you can do with spacebar, otherwise you go to PageUp/PageDown. And if you desperately need granularity, you can grudgingly go to the mouse wheel.

Corollary: One quirk with the keyboad methods is that the content pane must be in focus, which doesn't happen by default on page load in Firefox, so I first have to click inside the content to get this activated. A pet peeve.