http://clinicaltrials.gov/ct/gui/show/NCT00260442
Here is what happened...
0 eggs= 2% increase in muscle mass & about 14% increase in strength
1 egg= 1% increase in muscle mass & about 9% increase in strength.
Now as you can see, not much on one egg.
Here is the result with 3 eggs
About a 4% increase in muscle mass & a whopping 33% increase in strength
Total daily cholesterol for all 3 groups was
200mg
400mg
800mg
This is where there are debates about cholesterol. Sure, it can be bad, and can be worse if we already have problems. The upside however, is it is critical for maintaining test levels.
Some research also shows that a low diet in it can impair muscle mass and strength.
Now some eat tons, and we aren't all saying you have to eat 12 a day. While they are good, yeah that might be over-kill and you can get protein from other sources too.
BUT as far as the cholesterol is concerned, if you are good to go, i'd say eating 3 eggs per day is prob a good thing. Again that study was 12 weeks, and I cant say what it would be if you ate 4 or 5 or even more.
The point being more than anything is that the cholesterol is necessary.
So the answer to your question regarding what else besides protein... there you have it. They are also packed with many other nutrients, and flax fed chickens that lay eggs produce eggs that are high in Omega-3s as well.