I have been needing a BPMN and a UML 2 stencil for Visio 2007, and, truth said, I think I found my happyness in the following stencils :

For UML 2, I found one at softwarestencils. There are plenty of different stencils, even for Visio 2007. It offers all the shapes, but for some of them, you need to change the properties of them to have them appearing on your design surface. So, for UML 2, go there.

Regarding BPMN, the one proposed by Tyner Blain is a goodfit and it seems, at a first glance, it fits all my current needs. It offers all the BPMN shapes, the only thing missing, maybe, are the swimlanes.