I'll admit that I'm more into puzzles and brain games than I am into, say, poker. Don't get me wrong. iPhone poker is cool, but the word game Wurdle is the one I can't put down as I nearly miss my bus stop.
In Wurdle ($1.99), you drag your finger in any direction over adjacent letters in a grid to form as many words as you can before time runs out. The grid size, word length, game duration, dictionary, and even tile color are all customizable. Wurdle keeps track of high scores and the longest words you find. By far the most shaming, and also useful, feature is comparing your hits with a long list of misses. How I could get "remand" and completely miss "mafia" and "trainee" is challenge enough to play again. And again. And again.
Brain Toot($0.99; not to be confused with the free Lite version) takes you out of Wurdle's English class with four tests each in four disciplines--math, memory, vision, and cognition. You choose your difficulty level and begin running through a fairly simple routine. The beauty of Brain Toot is that it reveals your weaknesses as quickly as it does your strengths. Maybe counting change is a piece of cake, but memorizing a screen full of numbers has you banging your head against the iPhone. Brain Toot is also a good call for entertaining the younger folk and slipping some learning into the dead time of their day--or yours.
The free EyeTricks app is a brainteaser in the biological sense. Governed by your noggin, your eyes think they see one thing. EyeTricks reveals that they've been duped by an illusion of lights, angles, and perspective. While the application feels more focused on kids than on adults (unless you, too, love SpongeBob), it's amusing to see where your visual sensors lead you astray.
I'm sure you have your own favorite exercises for toning that fat lump of gray matter. Shout them out in the comments.