I got this gem from Class Strength:
A person has 2 branches of bananas, each branch having 50 bananas on it. She has to cross a vast sea in 50 boats (since each boat will only go a short distance, after which time the rider must switch to a second boat, then a third, and so on until the 50th boat finally reaches the other bank). There's one condition: each boatman must be given a banana per branch that he carries. Obeying the conditions stipulated strictly, it would not seem that the poor rider cannot make it across since all 100 of her bananas would have been exhausted as she pays the unscrupulous boatmen. The clever lass, however, strikes upon a strange idea by which he can get across (and even bring a few bananas to her family!) Can you figure out how she did it?