Edit: I choice the answer with highest score by December 06, 2012.
This is a soft question.
The concept of (deterministic) algorithms dates back to BC. What about the probabilistic algorithms?
In this wiki entry, Rabin's algorithm for the closest pair problem in computational geometry was given as the first randomized algorithm (year???). Lipton introduced Rabin's algorithm as the start of the modern era of random algorithms here, but not as the first one. I also know many algorithms for probabilistic finite automata (a very simple computational model) discovered during 1960s.
Do you know any probabilistic/randomized algorithms (or method) even before 1960s?
Which finding can be seen as the first probabilistic/randomized algorithm?