Help me get the lay of the land in Canon lenses

I've got a T4i/650 with the 18-135 STM kit lens on the way.  I've been a Nikon shooter until I sold my modest kit a few years ago so I don't know the Canon lenses as well as I might.

So help me start to get a grip on the EOS lenses please.  What are the legendary lenses? The hidden gems?  What are the used lenses I should look for?

Not looking for a particular need, just a general overview so I know what I might want when the need arises.

TIA, Tony