Write software for AstroGrid. At the moment, this is mostly Java Swing clients, although I've been more involved with server-side XML, SOAP and databases in the past:
Workbench - A desktop application for working with the Virtual Observatory. It can explore data resources, query remote catalogs, and construct workflows to automate tasks.
Astro Runtime - Client-side middleware that gives uniform access to all Virtual Observatory services, from all programming languages.