Many computer programming languages. I don't seem to have the knack for real languages.
Photography, Painting, Writing. Weird Tales, The Institute for the Preservation of Credible Pseudoscience (Fictional).
Chess. Artificial Intelligence. Artificial Stupidity.
The Perception of Meaning where there is None. Paranoia.
Game Theory. Games. Comics.
Accessibility and Usability, Metadata and Web Semantics (Microformats, RDF), Search and Navigation, Portals and Portlets, Syndication and Content Distribution.