If you are looking for actual test instruments use PsycTESTS. This database is a respository of testing instruments in psychology, the social sciences, and education. The drawback is that the tests are often not the famous or well-known tests you read about in the literature.
If you are looking for reviews of tests e.g. what are the best tests to use for a particular purpose than you want to use the Mental Measurements Yearbook with Tests in Print. This resource reviews test instruments and also lets you know if the test is available. Please note: MMYB does NOT include the full-text of the test instrument. It includes a review and where to purchase the actual testing instrument.