Using the Spaces Menu
When you turn on Spaces, you can also enable the Spaces menu in the menubar (via the "Show Spaces in menu bar" checkbox). The Spaces menu is helpful in two respects. First, it provides another way to switch between spaces. When you select it, you can immediately jump to any space by selecting that space's number.
Probably more useful is that the menu always displays the number of the current space. If you're working with a lot of spaces, this is a must-have feature because it can be easy to forget just how many spaces are open and where they are in relation to each other.