The "Future Research" Option - This is the most reliable way to find yourself a topic. Start with articles from the current issue of the most relevant journals, and look at the end for the part where they discuss the limits of their work and the next steps that geographers can take to expand or further this line of inquiry. Then figure out if you can take that step. This method has two advantages: it guarantees that you'll be participating in a scholarly conversation, and it doesn't require any bolt of inspiration. It also has two drawbacks: these next steps are often extremely challenging and/or expensive - there's a reason the original researchers didn't do them - and many other researchers are also trying this method, so your contribution will have competition.
The "Me-search" Option - A perennial favorite among academics in all the social sciences, this is the process of identifying a current hot debate or theory in geography and applying it to your own community. If you can figure out a way to make the connection, this is often a good balance of feasible and cutting-edge.
The Contrarian Option - Keep up with your course readings, skim the current journals, and wait for something to strike you as just plain wrong. Maybe the author overlooks a counter-example you know well; maybe they should have used a different statistical technique. This method of topic selection requires serendipity but is highly motivating if you stumble into it. It can often be combined with "me-search" (when what doesn't fit in the author's argument is your own community).
The Overlooked Gem - This is a method of topic selection particularly appropriate for courses like GEOG 300 where you learn about the history of the discipline. You might encounter a once-prominent theory or method that has fallen out of fashion in the current literature but has a surprisingly relevant insight to an emerging contemporary issue. Making that connection can make for an interesting topic.