jack of all trades, master of none. I find (with very little exceptions) that the more a lens can do, the less it is good at any single thing.
While you can get something like an 18-200, I would go with what you enjoy the most of right now and get a decent zoom that is made more for that. then slowly build up your lens collection as you go.
landscape usually means wider angle lenses. I love my 10-22. 18-55 could be good, but might want to upgrade the lens to a 17-55 or something similar
wildlife means longer lenses, in the 300-600mm range. For quality glass, this can be very expensive.
macro is specialised. With your T1i, look into a prime lens such as a 60mm or 100mm macro. Make sure its a true macro and does 1:1 ratio. Alot of lenses say they are macro, but they are more closeup.
Also, check the beginner forum, there are other threads on similar topics. And use the SEARCH function to help find older posts that are about the exact same thing.