Based at George Mason University, the CHNM aims to use "digital media and computer technology to democratize history." This is a good centralized location to find online tools for digital humanities research along with examples of digital projects.
Based at the University of Virginia, the VCDH seeks to advance historic scholarship as it facilitates the creation of digital history projects and creates new applications for current and future researchers. This site includes a list of the digital collections created at the VCDH.
This center is in the University College of London and aims at harnessing digital technologies to pursue new avenues of scholarly research in all areas of the humanities. The Research Projects page provides examples of the wide variety of projects in the field of Digital Humanities.
A robust list of digital humanities centers in the United States can be found in Appendix B of this 2008 survey. Since new digital humanities centers open every year, this static list is not comprehensive but is a good starting place, including centers established before 2008.