2. Advanced Task Killer
One of the realities of having a multitasking mobile OS is that you have to manage your apps so that they don't hurt performance or battery life. Advanced Task Killer (ATK) is my favorite on Android. It even comes with a widget that you can tap once to kill all open apps and you can also set up ATK to kill all apps at periodic intervals. Some people will argue that task managers are irrelevant and unneeded in Android, but I still prefer to use ATK.
If you'd prefer to view this as a list instead of a photo gallery, then see the companion blog post.