Access Flickr with Ruby and Flickraw
Flickr is a well known site for sharing photos and it is one of the most popular sites that published their services and allow to use them freely.
It is not necessary to work on a photo uploader, photo printing site or a mashup solution to become an user of the services. Sometimes it is interesting enough to get a list of your photos URLs and show them in a favourite flash photo viewer on your own web site.
There are several libraries for Ruby, one of the most up-to-date is Flickraw. Unfortunately it is not mentioned on the official Flickr services page, although it works smoothly, has a good documentation and is actively maintained (btw. the RubyForge project page is outdated, but the github page is up-to-date).
(There is more where this came from … )