You can use spotlight to search for things on your iPad or the web, but you can also use it for starting apps. It is a super fast app switcher when you use an external keyboard.
Press ⌘ Spacebar to open Spotlight (just as on your Mac). Type the first letters of the app you want to open, use the up-down arrow keys to choose the app and press Enter to open it. If the app you want is at the top you can press enter without having to choose it with the arrow keys.
When you have got the hang of it it really is a very fast way of switching between apps.