Conundrums is a striking new book, designed by Harry Pearce of Pentagram, that presents a collection of typographic puzzles constrained by three simple rules: one box, two colours, a single typeface. The typeface used is AG Old Face designed by Guenter Gerhard Lange in 1984 for the H. Berthold AG type foundry.
Beautiful. You can grab a copy for only $10 at Amazon.
My Typography II class at Pratt pretty much consisted of doing this kind of exercise all semester and then, as the final project, designing and constructing a book to compile the best of them.