My favorites are the same as many have already said....
1) walk in coop
2) auto chicken door....this is such a great invention!!
3) poop boards
3) outside nests with hinged door to collect eggs
4) electricity....lights I can switch on so I can see in the coop on these long winter nights and plugs for a water heater to keep the water from freezing.
5) water spigot at the coop.....love it in the summer and it's also near the veggie gardens so I don't have to haul heavy hoses so far.
6) three windows-two are double paned old basement windows so they are warmer in the winter but can open up wide in summer.
7) vinyl floor-so easy to clean.
8) Insulated-keeps it cooler in summer and warmer in winter
9) adjustable venting...have 6 vents that can be adjusted to various degrees of open or closed depending on weather conditions
10) painted inside with gloss paint-much easier to scrub off the poop they seem to get everywhere
Good luck with your new coop. I had fun building mine especially after finding all these great ideas right here on BYC. This is such a helpful forum!!