Noteworthy Projects, Dude

Nokogiri (git)
Co-author and maintainer of the premier Ruby XML/HTML parsing library. Fast, and with standards-compliant support for CSS and XPath.
Mechanize (git)
Co-maintainer of the premier Ruby web scraping library. Check out the brains on Aaron.
Loofah (git)
Author and maintainer of this HTML/XML manipulation and sanitization library, which uses Nokogiri for parsing and document manipulation. Prevent XSS attacks! Forget you ever knew XSLT!
McBean (git)
Author of this nascent Ruby library whose goal is to transform documents seamlessly between markup formats including HTML, Markdown, and Textile.
Lorax (git)
Author of this early-alpha (unstable) XML diff library for Ruby. "I am the Lorax, I speak for the trees."
ruby-ffi (git)
Contributor to Ruby's Foreign Function Interface project, for JRuby and MRI.
aintablog (git)
Wherein I once again merely add incremental value to someone else's way-cool project (in this case, Pat's), and get rewarded with core contributor status.
ActiveHash (git)
Co-author of this Rails gem which builds ActiveRecord-like models from non-database, readonly data sources like a Hash, a YAML file, or any custom data file format you may have laying around.
git.rake (git)
Set of rake tasks to make it easy to keep your git superproject in synch with multiple submodules. If that sort of thing floats your boat.
git-instaweb (commits)
Ever run git-instaweb --httpd=webrick? No? Oh. Well, if you had, you'd be running my codes. Sigh. Carry on.
flexible-js-formatting (git)
Contributor to Baron Schwartz's super-fast javascript library for formatting and parsing datetimes and numbers. If you use Datejs, you will be blown away by how fast this library is, thanks to its badass use of badass javascript metaprogramming. Read Baron's original article for a taste. Badass!
Rinari: Ruby on Rails Minor Mode for Emacs
Contributor to Rinari, the most excellent rails mode for the most excellent editor.