The 500px Ruby wrapper by Chris Micacchi has been designed to interact easily with the API capabilities of search, retrieve, and upload photos. It aims to reuse HTTP connections. 500px is a community of photographers who can showcase their projects, discover new photography styles, and find royalty-free art.
Instagram is one of those early adopter favorites that quickly crossed the chasm to more mainstream users, at least within my social network. Take that popularity, mix it with an apparent desire to buy shirts, and it was inevitable that someone would use the Instagram API to create wearable mashups. In fact, there are at least three such services, each with its own twist.