When iOS 4.0 was released with multitasking for the iPhone and iPod touch, Apple removed the convenient volume slider control from the double-click the home button menu. Many users were not happy about this and it looks like Apple has listened.
The volume slider has returned in iOS 4.2 and it is accessible by sliding the multitasking dock all the way to the left. One slide to the left takes you to the standard media controls and orientation switch from iOS 4.0/4.1 and one more slide takes you to the volume slider seen above.
AirPlay is also now easily accessible from the iPhone/iPod touch multitasking dock (thanks, Drew). Screenshot after the break: