1) Instagram: http://instagr.am/
Why: Take photos with your phone and then apply really awesome pre-made filters to them with just and share them with people.
2) Postagram: http://postagramapp.com/
Why: This allows you to take photos from instagram OR your facebook profile or photo stream and send a really nice postcard to anyone within the USA for only 99 cents. The card has the photo perforated, so your recipient can just pop it out and keep it!
3) Sincerly Ink: http://sincerely.com/
Why: This is another post card sender that allows you to do higher end cards, like Christmas Cards using your phone photos for 1.99 each. Very personalized one on one cards. I love when digital begats real.
4) Tout: http://www.tout.com/
Why: People's attention spans have gone from 60 seconds to 15 these days, so this is a great way to share moments in your life with friends or the general public. It takes 15 second videos and plays them in a story stream. So if you start someone's tout at the beginning, you can see their life in 15 second moments and sort of get a digest of theme in a very visual way.
5) Hipstamatic Disposable: http://disposable.hipstamatic.com/
Hipstamatic turns your phone camera into an old timey instamatic like the one you had if you were born prior to the 90's. This spin off of that app allows you to share a "virtual roll" of film with another user and neither of you can see the pictures till you shoot the roll and develop it. It is a great way to shoot a vacation or event and then share the pictures later and get that unexpected thrill you used to get when you had to wait to see the photos.
Some close runner ups are: