Google Scholar can be a useful searching tool, particularly when it checks against the electronic full text holdings at FSU. This link requires you to log in with your FSU e-mail information-- but it's worth it!
Indexes largely U.S. theses and dissertations from roughly 1861 to the present. The abstracts are searchable and are the most helpful aspect of this resource. Provides full text for many dissertations.
Many universities now make dissertations freely available on the web. Use Google Scholar to either find citations or see if those citations located in Dissertations and Theses or PsycInfo are available freely on the web.