Custom Menu (+ Desc) Widget is just like the Custom Menu widget built into wordpress, except that it also pulls the descriptions.
Slightly modifies the built in Custom Menu widget to also show descriptions. Adds a span class of "CMWdesc" for easy styling. Borrows code from here as well (for the walker class rewrite). No guarantees of fitness for anything, I just couldn't find a plugin to do this simple thing so made one myself. Hope you like it. Note: Make sure descriptions are enabled in the screen options of your Menus admin, then edit to suit under each menu item. Add the widget and voila.