What is the best online discovery you have made in the past year?

It might be an online store, a song, a video, a person, a game, a product or involve a theme (a historic event, the natural world). It may also be available offline (a brick and mortar store, for example) but you discovered and utilize it primarily online. Something that you like so much that you visit it regularly, have shared it with others or would like to.

What is it you like about it? For example, is it entertaining, educational, weird, fascinating, silly or serious? Has finding it benefited you in a particular way? If you became a Jelly this past year, Fluther might be a good example.

Please share your favorite online discoveries of the past year.