iRelay! (US$0.99) is an interesting photo sharing app that provides some features that aren't native to the iPhone.
Using the app, pictures on your phone can be grouped by collection, activity or person. A link can be posted to the galleries, and that link can be shared over email, text messages, Facebook, Tumblr or Twitter.
Photos are sent at full resolution, and you can see the galleries of friends who are also using iRelay. You can send multiple photos at a time, but only via email.
iRelay! solves these issues neatly. Storage uses your iCloud allotment, and links expire in 14 days.
One thing I've noticed, and I think it is an issue. When I email a link to a gallery it can't be opened on a Mac using Safari or Chrome directly. Instead, the browsers download the link, which can then be double clicked on. That seems a bit of a nuisance. Even right-clicking on the link doesn't do the trick. On an iOS device the link works perfectly, and the gallery appears with an expiration date.
iRelay! is a pretty nice solution to getting your pictures out to friends and family in a straightforward way. Not everything is intuitive about using the app, but comprehensive help is built-in and easy to understand. The app is iPhone only and requires iOS5 or greater.
Check the gallery for some screen shots.