I think I've found where I'm going to have my next set of invitations made- and it's not a bricks and mortar store. It's an online retailer called Paperlesspost.com, they specialize in online invitations that look like you should be receiving them via Postal Service and not E-mail.
PaperLessPost.com allows you to fully customize your online invitations- from paper selection all the way to motif. It doesn't matter the occasion, you'll definitely be able to find a fantastic custom card to send to all of your guests.
You pay per stamp, and it's super cheap. For example; 250 stamps will cost you $10.00 (real postage stamp price equivalent: $105.00 + cost of invitations). Each stamp will ensure email delivery to a guest on your list.
This may not work for those distant relatives that aren't so internet savvy, so you might want to keep that in mind when writing up your guest list. It's also a great idea because you won't have to worry about anyone losing your paper invite and not being able to RSVP in time!