[Zikes]

Perhaps a nice card from https://lob.com/ with a QR code to the RSVP form?

[eric_the_read]

http://picturesofpeoplescanningqrcodes.tumblr.com/

[Zikes]

http://picturesofpeoplescanningmicrosofttags.tumblr.com/

[gcatalfamo]

I spilled my coffee!

[rsync]

"Perhaps a nice card from https://lob.com/ with a QR code to the RSVP form?"

Better to use an Oh By Code, which doesn't need a reader and can be written/read by humans:

https://0x.co