Check out the monarch butterfly, egg and larvae maps here, at the Journey North website. They also have all sorts of other cool maps for migrating animals, including hummingbirds and robins, and the timing of plants flowering.
If you want to observe the monarch life cycle yourself, plant some native milkweed in your garden, or stop by a local park, garden or roadside that has some. Look on the bottom of leaves for eggs, and also look for little holes (or big holes if the caterpillars are large). You can even report your sightings to Journey North, too, if you are in the Upper Midwest, Northeast, or Canada, where they want reports of the first sightings of the season.
All the following photos were taken by me in 2012.
If you missed it, here is an earlier blog post about the plight of the monarchs. I am happy to say that this looks like a promising start to this year's monarch populations.