Exposé within Spaces!
Spaces can be really great when you are working on multiple projects. If you don't know to exactly which space you want to go, F8 (the space shortcut) is usually the most efficient way of finding where is the stuff you want to work on. If you have a lot of applications on top of each other, it might not work as well. That is where you can use Exposé within Spaces. The application specific Exposé (used to be F10) doesn't work there, but the standard Exposé (used to be F9) works perfectly within Spaces!