There's a couple of threads already in existence which I think you might find useful, dozystrelok.
Best legal stuff to help relax.
Legal Party/Fun Drugs
I think the threads above already cover the broad 'what legal high should I take' question, and I am also somewhat concerned that the HR value of a thread such as this is fairly limited. BL's purpose is not to suggest what drugs someone should take, as different substances have different effects on different people, different safety profiles and interactions, and so on.
Already some suggestions have been made which have the potential for significant side effects, and I agree with the other posters emphasising the importance of being careful around legal/quasi legal substances. 'Legal' doesn't necessarily mean weak or safe. There's a wealth of information available on BL, and I can't stress enough the importance of researching carefully anything you're thinking of taking.
I think you'll find the threads above a useful place to start for general information. If after conducting some research you have some more specific questions on dosages, interactions, effects and so on of particular substances, asking in one of those threads, or creating a new thread, would be appropriate. I'm just not comfortable with the idea of asking so broadly 'what drug should I take'. I'm going to close this thread, but you're welcome to PM me with any questions/comments you may have, dozystrelok.