I plan on including a response card and stamped return envelope with my wedding invitations, but we have a wedding website for our guests to RSVP. Since not all of our guests will use the website, I think it's important to include the response card and stamped envelope.
I hate to waste a bunch of stamps if most people are going to use the website to RSVP, but I don't want to be tacky by not including a stamp.
What have you done?