There is probably a fansite that keeps track of these things, but I am willing to bet that 'Flashes Before Your Eyes' had the greatest number of Easter eggs than any previous Lost episode. For my part, I have never had to pause-rewind-pause so many times in my life. The entire episode seemed like one giant clue for viewers, and there are more than enough fan theories about what the primary message was.

I have no doubt that this list will be incomplete, but here is a list of the major Easter eggs that have been discovered so far:

The Numbers: Numbers played a huge role in Desmond's understanding of his abilities. During his revisit to the pre-island past, Desmond glanced at his bedroom clock, which read 1:08. These numbers connect back to the hatch, of course (Desmond entered the numbers every 108 minutes). Later, at the Widmore reception area, Desmond saw a deliveryman arrive with a package for 815 (the doomed Oceanic flight, as well as the numbers 8 and 15).