Power Strip - Multi-task AND keep your home screen app (From the Home++ creators)
I purchased this app on the weekend, and it's simply awesome.
The idea is that you can launch new apps AND access widgets without leaving the current app that you're running.
Power Strip also allows a bit of a pass-through to your home screen app, so that you don't lose any of that functionality either.
i.e. I'm running an app, but would like to turn on 3G or change the brightness, I can jump straight to my SwitchPro widget without "leaving" the application.
It costs 99cents, which to me is pretty trivial.