These are two popular tweaks available from Cydia's standard repository for $0.99 (USD) each.
Infiniboard: Vertically scroll your home screen pages. Add as many icons as you want to each page, and access them with a flick up and down.
In the Settings app, there are features of Infiniboard you can turn on and off (see photo). I like the ability to use a white or black scrollbar so that, depending on the color of my background, I can see where I am on the springboard. I also set the "Hide Behind Dock" to on, else it gets rather muddled around the dock area.
Infinidock: Infinidock is the ultimate dock scrolling and customization tool. Add as many icons as you want to your dock and scroll back and forth. Set how many icons per page. Give your dock pages.
Who needs to be limited to just six icons on the dock? With this tweak, you can put an unlimited amount on your iPad's dock and then scroll, just like springboard pages.
In the Settings app, you can set the number of icons you wish to show per page (see photo). This doesn't mean a limit on the number of icons on the dock, just how many will show in one page view. Do note that nine (9) icons is the highest you can display on the dock without having to scroll. But, if you don't mind scrolling … so what? The Paging function allows you to set your icons into groups versus continuous scrolling. As you swipe, your dock icons will move as one set.
I've always enjoyed these two tweaks and can't imagine my iPad without them. Both tweaks worked fine on my iPad1 running iOS 4.2.1 and they continue to work great now that I've upgraded to iOS 4.3.3.
Ultimately, it is hard to give these two tweaks an adequate description with words and mere pictures, so I've made a video of them in action. Much simpler, don't you think?
[ame="http://www.youtube.com/watch?v=Cz8kEO2DLdA"]Infiniboard & Infinidock[/ame]