There's a really good book on the topic of career planning (among other things), written by Cal Newport -- "So Good They Can't Ignore You" (http://www.amazon.ca/books/dp/1455509124).

Most people give the advice of "Do what you love and get most excited about" and this is, to some extent, the advice I would have given as well. However, when I think back to the work I've done and that has made me most proud in life, a bit chunk of it is simply doing new things, and pushing myself further than ever before. Cal Newport's advice is more along the lines of "Do what you're really good at, rather than only what you love."

Of course, this assumes you don't hate what you're doing. Food for thought.