Here is a cute way to add a touch of pretty lace to your invitations - doily envelope liners. You'll need to start by creating a template that will depend on your style of envelope, make sure its a couple of centermeters smaller than the actually envelope so it will fit easily. Just mark out the shape on the doily, cut and glue to the inside of the envelope.

Square or rectangular doilies are perfect but can be a little tricky to find. You could get the same effect with a lace paper stamp like the Martha Steward doily lace punches below.