So, as I posted before, we purchased our invitations from Bella Figura and had a really wonderful experience with them. We then picked out coordinating envelopes and envelope liners from Paper Source. Of course, we picked paper that didn't come pre-cut so my honey cut out 125 envelope liners, but we really think it was worth it. I "hand addressed" them all by tracing over a the address we printed directly onto the invitation--which worked out really well. And, finally, we ordered the Fling return address stamp from PaperWink.
PaperWink was really great to work with (although the stamp's arrival was delayed due to a mix-up at my apartment). But last night I was able to stamp all the back flaps with my parents' address, as shown here:
And today they will go in the mail--Yay!!