It has to be something new. You can easily find a list of thesis topics by googling this: computer science, thesis topics, list
But those are OTHER people's topics. They have already been done. I think you should look at 1 article that interests you, and look at the LITERATURE REVIEW. Make sure this article has a lit review, and make sure it was written in the past year or two. 2010 or 2011...
The lit review will explain to you all the recent research that has been done in a particular area of comp sci. That is an ongoing discussion, and it is time for YOU to contribute to the discussion.
Read that literature review 5 times, and then go find one of the articles cited in it, and read the lit review in THAT article. Take some notes, and come up with your idea. No one is better able to do this than you; we all have to start by reading the lit reviews.