I thought I would mention this free program for Macs. It creates a drop down menu which lists all installed VMs. Very handy and works with OSX 10.4.4 - 10.9.2.
https://www.macupdate.com/app/mac/34155/virtualbox-menulet
edit: It appears this program causes some error messages to be written to the VBoxSVC.log but it doesn't affect anything.