Digital Commons Network brings together the digital repositories of hundreds of colleges and universities worldwide to provide access to full text academic content. After your initial search scroll down on the left side of your search results to "Publication Type" and choose "Theses/Dissertations".
The Networked Digital Library of Theses and Dissertations (NDLTD) is an international organization dedicated to promoting the adoption, creation, use, dissemination, and preservation of electronic theses and dissertations (ETDs)
OATD.org aims to be the best possible resource for finding open access graduate theses and dissertations published around the world. Metadata (information about the theses) comes from over 1100 colleges, universities, and research institutions.