Be sure to contact the college or university you will be attending to find out if a specific test is required or to request a printed registration application. For additional information, you can check out the The Tests You'll Need page.
Here are links for registering for commonly required tests:
THEA (Texas Higher Education Assessment)
PSAT/NMSQT (Preliminary SAT/National Merit Scholarship Qualifying Test)
SAT (Scholastic Aptitude Test)
CLEP (College Level Examination Program)