I've been using Responsive Nav by Viljami Salminen for a few projects recently. It's the quickest way to add the trendy menu to your site.
Add in the fact that is has no external dependencies and uses CSS3 transitions you've got a clear winner. It's fairly customisable too.
ProTip: Couple it with Chris Coyier's post on Three Line Menu Navicons to get that perfect looking burger menu icon.