The world of development is always changing, and you either keep up or get out, for the most part. In 2011, there are a number of technologies that are not quite "must have" skills, but being proficient in them could make a big difference when you want to stand out from the pack and not.
In no particular order, I think that developers who learn Ruby, mobile development, Silverlight/WPF, HTML 5, and Java 7 (I know, some of these are not finalized yet) will be setting themselves up quite nicely for long-term career growth quite nicely. For me, I'm learning more about mobile development as well as Silverlight since I'm doing Windows Phone 7 work.
Which of these technologies would you learn if you had the chance? If you're interested in learning a development technology that I didn't list, tell us what it is in the discussion.
Justin James is the Lead Architect for Conigent.