Multifl0w is how we feel Apple should have implemented multitasking into iOS in the first place. It works quickly, beautifully, and efficiently on jailbroken iPhones, iPod touches and... iPads! The app collaborates with the free "backgrounder" app from Cydia and displays up to 9 apps at a time. You can get the app on the Cydia store for $4.99 and you can get more info here (http://www.multifl0w.com/) via the official site, you can look here (http://www.rockyourphone.com/index.php/multifl0w.html) too.
Multifl0w - Exposé-like multitasking on iOS4 and iPad (http://www.youtube.com/watch?v=pcIORhb8NfQ&feature=player_embedded#ws)