A few of my favourites that immediately come to mind:

 - Janich, Klaus. _Topology_
 - Carter, Nathan. _Visual group theory_
 - Lawvere, F. William and Stephen H. Schanuel. _Conceptual mathematics: a first introduction to categories_
 - Aigner, Martin; Ziegler, Günter. _Proofs from THE BOOK_

Also, in their own weird way:

 - Steen, Lynn Arthur and Seebach, J. Arthur. _Counterexamples in topology_
 - Nelsen, Roger B. _Proofs without words: Exercises in visual thinking (series)_