When you have a lot of pages i prefer to have drop down menus for each major topic and then for items in those drop down menus (when you mouse over) that also have many pages have their own drop down menu. For example
section1 >
S1.item1>
S1.item2> (then say S1.item2 has a few pages in itselft)
S1.Item2.page1
S1.Item2.page2
S1.Item2.page3
S1.item3>
etc....
You can also do that for a vertical menu.
Thats just my preference though, you can also do other menu styles to handle many pages. You could have a fixed vertical main menu that holds the main sections then each section has it's own vertical menu. If that makes sense.
There my thoughts
Oh and a problem with the drop down menus when you mouse over them is that they can be a bit harder to code if you are not experienced. Where as a fixed menu is much easier. You can find some preset code for navigation menus if you are coding it yourself, that could help a bit, might take a little while to find though.