There are many eggs on Halo but these are the ones I found myself:

(No.1) In foundry on forge spawn a container single, doesn't matter whether its open or not.Now go into human mode and look at the side that doesn't have the UNSC emblem on it, now look carefully, if you see something it will be in the center of the of that side.You will see either one or two things, a panther with paws up like he's going to attack you, or a little statue of Anubis one of the egyptian gods.

(No.2) This one might just be my imagination getting to me.On Sandtrap go to the the side of the map that has the shorter arch, walk to the middle of it to where you are standing right in the middle of it and are facing thr other arch, it should form the face of yosemite sam from Looney Toons If you line it up correctly the taller arch and the pillers will form his hat, the walls on both sides of the hall leading down the middle should form his moustache. If you can't see him by that time you're not going to see him.

(No.3)Get two SMG's and find a nice flat non- movable wall best done on Last Resort. Walk up to the wall, get as close as possible, and fire EXACTLY 100 bullets from both SMG's into the wall and in doing so it should spell out one of the game developers names.

(No.4)The Next one is located on the campaign level "The Storm".It includes two eggs the first one is getting up on the beached ship get a brute shot if you can find one a vehicle(ghost works best).Get the person that has the bruteshot get on top of the vehicle that is being driven(once again ghost works best)now back up to where the vehicle being driven is against the
wall, then drive off the little walkway there then when you get as close to the ship as possible while you are still up in the air have the other person brute shot jump of the vehicle and land on the upper deck of the ship.Now if the other people in your group want to see this to tell them to kill themselves. Now watch on as they commit suicide for your pleasure. They should respawn back on the ship with you, now go below deck and you should find a picture of a pirate and I think it says something about tresure.When you and your friends are done looking at pirate booty, jump off the ship and go as far back as you need to where you can get a good view of the end of the ship, and what do you know , it looks like master cheifs helmet.

(No.5) Now you don't have to believe me about this one but it is true, on the first level, I don't care how you do it ,because I don't even know how I did it,somehow glitch underneath the level, and if you actually do it you should see a gigantic egg that says "Prepare for the WARS" in a font like that of which you see the numbers on the cover of the halo games.And on the
the top of the egg once get close to will see a grunt.When he see's you, he will run to the other side of the egg.A couple of seconds later he comes back with a tuxedo and a Top Hat on(I am not lying no matter how unrealistic this sounds) and he does what I assume is the the CHARLESTON which is a type of dance.No Kidding.