iPad (jailbroken): iOS has never had really solid multitasking abilities, but OS Experience is a new jailbreak app for the iPad that allows you to multitask in a way that's similar to a desktop. You can put apps side by side, drag apps between desktops, use live previews and more.
As the above walkthrough put together by iDownloadblog shows, multitasking with OS Experience takes a bit of time to get used to, but it works a lot like it does on a desktop. Essentially, you're given a desktop mode where you launch as many apps as you want in one desktop area. You can have Evernote and Safari running on one screen so you can take notes, or have YouTube running next to your email if you want to watch a video while you type. It's a surprisingly powerful app that definitely makes multitasking on the iPad more useful.