How to select a Master's thesis topic if your advisor won't suggest one?
One approach is follows:
Find one or two good recent PhD theses in your chosen area. Read these thoroughly. As you read, write down every question that pops into your mind, write down every time the author states that something is left for future work or needs further investigation. This will have a dual effect. Firstly, you will get a good introduction to a particular research field. Secondly, you will have a bunch of questions that need to be investigated.
Prune trivial questions, non-sensible ones, etc.
Next, organize your questions thematically and see whether you can find a common thread to these questions, something that could form the basis of your research.
Remove any questions that do not fit will with the others.
Based on the remaining questions, formulate a couple of coherent questions that your research could address.
Write a plan to address these questions.
Work through plan.
Write thesis.
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.
I would look what are the domain of interest of my advisor, see what he dose, and pick a thesis on one of that domain (In case I can run in trouble he can help). But I will take care to be a topic that I can also find interesting.