500px is a highly regarded photography site which only seems to showcase the most spectacular pictures. It's like Flickr but with a more professional presentation. When you go to the homepage you're given tiles of the most popular pictures right now which are just downright amazing.
500px has had an iPad app for a year now, finally they have released an iPhone app. Who knows what took them so long but boy is it good. The design of the app itself is beautiful. Following their style minimalistic style, the app is really minimal, making the content the focus of the app.
When logged in with your account you can comment, like and love pictures however you please. You can also look at the info for a picture, including EXIF info, what category it is placed in, who it was taken by and when it was taken.
I'm sure many 500px will be very pleased with an app for their iPhone now.