I don't think you need a plugin. WordPress isn't really set up to create non-linked parent menu items but here is the trick I use when I need to.
If you haven't already, maybe review this first: Appearance Menus.
–While editing your menu, go to the Links box on the left sidebar. Type in a fake link address for 'URL' and the title of your dropdown menu item where it says 'Link text.'
–Drag your new link over to your menu and place it where you want it.
–Click the top right arrow on that menu item to open up its options.
–Delete the fake link address from the 'URL' field. (this stops it from being a clickable link, and means it's only a dropdown menu parent)
–Move your child menu items underneath the menu item you just created so that they become a dropdown menu.
–Save your menu, make sure it's assigned where you want, and check your site.
Aside: Here is some information on shortcodes, though it may be more than you need.