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:
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.
Here is how they look with the simple theme: