You'll be amazed at how much the choice of Master's thesis will influence your long-term interest in the field, prospects for jobs within and outside of academia.
I'd suggest picking up some mainstream journals or magazines in your field and see what is currently trendy in the field, and what are bread and butter topics. Having a birds eye view of what's going on in the field allows you to be strategic about your topic, with the goal of planning a successful career.
Most likely, a successful career is one that will hook into an existing community of researchers in a topic, with a reliable source of funds that pay for conferences, departments, and students to populate them. A strategic topic is one that has the potential to make an impact in the field, and has the potential to cross-over into related disciplines, or even to have practical applications to real people (god forbid).
Finally, and most importantly, choose a topic that gets your blood flowing. Your master's topic could very easily become a PhD topic, which could then become a career focus. A lot of grad student burn-out is the result of students reaching their limit of interest in a topic, and thus deciding they've had enough.
As you survey mainstream and more specific literatures, be aware of what problems and topics get you excited. Choose something that you actually get excited about, that you can't stop thinking and talking about, and that you can even get other people excited about. That's the topic that will keep you going when you get stuck in the muck of research and don't know if you can keep going for another year.