Mark Wunsch’s Tumblr Gem is The Shit 

Now this is cool. More than just a Ruby API wrapper for Tumblr, Wunsch's tumblr-rb gem provides a nice command-line interface for creating new posts. And in the grand *nix command-line tradition, if you're in a hurry it's easy to pipe text into it straight from your favorite text editor. Posts can be marked up with YAML frontmatter, a feature straight out of Tom Preston-Werner's wonderful Jekyll static site generator.