Should I Become an Expert in a Single Technology/Platform?

I'm at the beginning of my career, working as a web developer for a small company. I would really like to advance my skills, but I was wondering, in what direction: horizontally or vertically?

In other words, should I learn a lot about a small number of technologies, or should I expand my knowledge to a lot of fields, taking the risk of knowing stuff only superficially.

Both approaches are fun. While learning a lot of stuff superficially is easy and not too frustrating, becoming an expert in a specific technology can also be fun, since I get to choose that technology...

But what I would really like to know is which path to take in order to become a great programmer? And which is the path to a more lucrative job? Are they the same?