We've had a couple weddings now that pass out cards for apps that they have signed up for, and ask their guests to include their wedding photos. GREAT IDEA!! If you're an Instagramer, I highly suggest creating a hashtag, and posting for your guests to use. But not everyone is! Or, even knows what a hashtag is... So I checked out this site, and HIGHLY suggest it to every couple!
Seems like this is the Facebook and Instagram of Wedding photo apps. You can create different albums in your profile; share your Bridal Shower, Engagement photos--whatever you choose. And its FREE! You can share the app and information with your guests via Facebook and email. Also, there is the option to print invites for your guests to use the app. The only downside, you can't upload video.