While it's easy to talk about satellites orbiting the earth, it's another thing to actually see the number of satellites up there. This post links to a website that has a good, interactive graphic showing all known satellites orbiting the earth divided up by their orbital height.
To see how the satellites move in relation to each other, press 'Q' and press the space bar. Just be warned, it might melt your browser. :D
If you have a few minutes, I suggest you look around here. It's interesting even if you're not doing a sci fi book.