What Dual Mount SD Widget does is quite simple, but extremely helpful: it allows you to mount your SD card to your phone and PC at the same time. This means that you'll be able to transfer files to and from your phone via USB without losing the ability to run apps that are stored on your SD card. Of course, in order for this widget to do its thing, you need not use the built-in mounting option, and you must disable Android's auto-mount (but the widget includes its own auto-mounting option).
This app is for rooted devices only.
Good and Evo]