My "Title" here is "Snr HTML & Graphic Designer" (how pants! I wanted "Creative Developer" but that's another story)
I specialize in Graphic Design (Including print) as well as CSS/HTML/Web Standards (which covers eveything from DTD Generation to Usability and Accessibility).
I've spent some time too looking into expanding my abilities... I'm a little ropey at Flash, know a fair bit of PHP/Javascript and that's about as far as my "extra" abilities go.
I agree with Mik, If I were to employ my own staff, I'd choose specialists over "jack of all". They wanted me to be a "jack of all" here, but I had to fight hard to get my current role into a "specialism". I still have to do Project Management, Customer Services and all the other bolloxy admin stuff, but I also get to spend a majority of my time doing R&D as well as Design/Build.
Given the choice to expand my "skillset" I'd go with Programming... ASP/PHP/JSP are definately becomming more and more in demand as well as .NET and it doesn't hurt to know some of these from a designer's point of view as it gives you more confidence when having to tweak a page a developer has bastardised!
Other than that, again, as Mik said, go and fine tune your design skills. Study Colour Theory, Application Layout, Computer/User Interaction, Golden Mean, Aesthetics, CSS and Usability and become a "Specialist".