I'm not aware of a universal website. The best way to choose a standardized instrument would be to decide what you want to measure and then look for a systematic review of instruments that purport to measure it. For example, there are a number of instruments that claim to measure health related quality of life. There are reviews that compare the instruments and point out strengths and weaknesses of each. Similarly, a number of scales for depression exist and there are reviews that compare and contrast the various instruments. A good literature review in your field will give you some ideas as well as the language to use in your pubmed search.