The human mind is infinitely fascinating. Dissertations in psychology will give you an opportunity to formally study various aspects of personality, relationship dynamics, addictions and intelligence, just to name a few areas. Also, according to the Bureau of Labor's Occupational Outlook Handbook, psychology will see a 22 percent employment growth rate from 2010 to 2020, faster than the average for all occupations, and job prospects will be best for students who have earned a Ph.D.
One way to get your dissertation idea for clinical psychology is to write about a specific type of clinical experience. One of the more popular types of psychologists at the moment is the sports psychologist, so a topic in that area would make an excellent dissertation. In a more traditional vein, a study of the efficacy of Jungian practice, which deals with archetypes, would be fascinating, as would a related study of the tarot and psychology. Sleep studies will also make for good research, as would studies of mindfulness practices, or even more traditional roles like marriage and family therapy, clinical social work or clinical counseling.
Another viable dissertation angle would be a demographic study of a specific population. For instance, writing on a specific ethnic minority or on women as a group lends itself well to the study of multicultural counseling or feminist therapy, in how either integrate with psychotherapy. You can also concentrate on a special population such as gay, lesbian, bisexual, and transgendered people (GLBT). Research on factors impacting clinical psychology or on how members of these groups are represented in the journal literature would be very valuable in the field.
Since psychology is a truly interdisciplinary field, one related to many others, research that borders on any of its tangential areas will be worthy of dissertations. For example, your Ph.D. research could look at the interrelatedness of psychology and philosophy, or even one of the hard sciences like biochemistry. On the other end of the spectrum, the intersection between psychology and religion and spirituality would be an excellent area of research. Also at your fingertips are the many types of literature review dissertation topics, where you analyze the content of published articles. Along these lines, studies of the literature of clinical psychology and counter-terrorism or of military clinical psychology could be enlightening.
Finally, there is great value in dissertations which better the teaching of psychology. These pedagogical dissertations help future professors develop better curricula, assignments and programs. An exploration of doctoral students' attitudes towards substance abusers would get a warm reception from your dissertation committee, as would any of these topics: the comparative success rates of extroverted versus introverted students, the role of gender in the classroom or the training of students in multiculturalism. Specialized dissertations, such as a 2013 autobiographical narrative by David N. Hunt which followed his success as a dyslexic student obtaining his Ph.D. Like the capacity of the human mind, dissertation topics in clinical psychology are virtually infinite.