I had to use Visio recently. Sadly, the product come with no proper stencils for UML2. I found some at softwarestencils.com and they were great!

It’s freeware but it’s not free:

Terms of use

You can use, copy and modify the template and stencils for your own use as you like. You are not allowed to redistribute, or make available to public, […]

There are no restrictions regarding the drawings you create using the shapes downloaded from this site.

Direct download link