Inkscape extension Shapes:
New options

This revision of Shapes adds some improvements:

Increase/decrease the size of the selected objects
Lets modify the size of the bounding box of the selected objects and thus modify the size of the resulting shapes.
Changes in Join circles
It is no longer necessary to apply Boolean operations to the resulting shapes, all options return a single object that is the union of the two selected circles.
New kind of union: Oval
Bug fixing:
Fixed a bug when copying style from objects with no style assigned