Finance topics for master in finance?

It really depends on what your goals are, as I see it (having done research before and, about to start some more research), below are the main goals or drivers of topic selection:
1. Career goals
2. Interests and passions
3. Academic achievement

You need to think about which one of these is the most important, for example, if career goals is your key motivation, then you simply pick a topic that is highly relevant to what you want to do e.g. if you want to work on capital raising then do an IPO study, if you want to be a trader or work in a hedge fund do something on developing and analysing trading strategies, if you want to work in M&A do a study on M&A... etc. On the interests side - it really pays to be interested in what you're doing because that will help keep you motivated. And of course if academic achievement is your goal (i.e. I would consider the height of academic achievement being getting your research published) then you'll need to choose a topic that is likely to be publishable, i.e. something that hasn't been done before (a new approach, a new dataset, etc)... and of course it's a good idea to talk to professors at your school as they may have some ideas.