What should I do if I have specialized in a useless research area? I am a PhD student in computer science, and chose to specialize in a research area that was interesting to me personally, but not interesting to most tech companies.  I am approaching graduation and I am not sure where to find a job.  What do I do now?
The specialised research area of your PhD topic probably has a wider range of related fields which are relevant to prospective employers.  I suggest identify those fields and use them to build your own resume, and also to identify prospective employers.  Search those terms in job sites and identify employers that way.

Unless committed to specifically continue research in a focused line of investigation, then in most cases, I believe that job seekers in your position are really looking for work which utilises the broader skills that they have generated through their post-graduate degree.  Try to take a step back to think of the skills you have gained.

The more generalised skills such as general subject knowledge, investigation, research community networking and research are more likely to be of value to your prospective employer than your expertise in your own specific topic.