Push-ups are unreasonably difficult, because my wrists are weak. I see my build type as mesomorph leaning to the ectomorph side of the spectrum, but I do have the classic ectomorph skinny wrists. There are exercises for that, the simplest of which is the dumbbell wrist curl. Dumbbells open up a whole new domain of other upper-body exercises as well, so I'd been considering getting a pair for a while. I love love love the concept of "speed adjustable" dumbbells, but for the price, I decided to just go with a pair of 15 lb. Sports Authority house brand "hex" dumbbells. 15# is a challenging weight, but not daunting.

dumbbell wrist curl ("wrist flexors", i.e. forearm)
dumbbell hammer curl (forearm, bicep)
dumbbell fly (pecs)
classic dumbbell curl (biceps)