There are several new trends appearing in the invitation world. The biggest one right now has to be the invitation pocket. This type of invitation is perfect if you need to include several pieces for your guest. It can display your invitation piece on the front and when turned around can hold pieces like your rsvp card, directions, places for your guests to stay or even a peacock feather. I have even seen them for destination weddings where the bride and groom included a list of things to do and bike rental tickets for those beach weddings.
This way your guests only have to worry about keeping up with this one packet and it holds everything together in a nice and neat package.
They can be ordered in several styles depending on how elaborate you want to get and come in a classic portrait style or a more modern landscape style. The pockets alone typically run anywhere from $1.30-$3.50/each depending on the style/color/quantity you choose. Be sure to check out talk with your local stationery store/designer to see what the best fit for your wedding vision and style is.