In time for spring/ Easter, Lemonade has some egg-stra special experiments and activities relating to eggs.
On the Strange Science page, there is the disappearing shell trick and how to unboil an egg: http://llemonade.com/transfigurationnoreturn.html
On the Advanced Experiments page, there are recipes for natural (food-based) dyes that can be used to dye eggs: http://llemonade.com/adultsci.html#natdye
On the Spring Crafts page are instructions for some egg-dying techniques (marbling etc.): http://llemonade.com/spring.html
And on the Wind Energy page is the classic egg-in-a-bottle trick for demonstrating the power of air pressure: http://llemonade.com/wind.html#press
Other egg activities:
Eggshell collage: like sand art, except you use crushed shells from coloured eggs as your medium. You can either brush a thin layer of glue onto your paper a section at a time and sprinkle one colour at a time, or use peel-back "sticker" paper and remove a section at a time to expose the adhesive and sprinkle the shells on the exposed section one colour at a time.
Test the strength of eggshells by cutting shells in half the short-way around the egg (unless you are very skilled at this, you will probably only get a half-shell for each egg). You will need 4 same-sized eggshell halves that are free of cracks in total, and several heavy books, at least one of which is hard-covered.
Place the shells in a rectangle slightly smaller than the hard-covered book. Begin placing books on top, one at a time, until the shells crack. How much weight did the eggshells support?
Be sure to wash your hands well after working with eggs!