70 qt. Coleman X-Treme with SS braid. Consistently gives me 75% BHE, and I’m happy with that…
You mean there’s a simpler version? ;D
70 quart Coleman extreme with braid here. Couldn’t be happier with it. 
I use a 48 qt Rubbermaid rectangular cooler that I made into a mash tun for around $29.00
http://www.donosborn.com/homebrew/mashtun.htm
It is modeled after Denny’s! 
Cheap, easy, and makes award-winning beer. Can’t complain.
I just started AG brewing with a 70 quart Coleman Xtreme with a braid for me. Works great so far, three 10 gallon batches under my belt.
The 50-something quart Coleman Xtreme here as well with the braid configuration straight from Denny’s site. I bought all the materials for a fancy drain valve, but since I couldn’t find SS washers, I went with the drilled stopper method and never looked back.
70 qt. Coleman Extreme w/ a 1/2" copper slotted manifold per Palmer’s specs. Self fabbed bulkhead. Routine 80% eff. using non-adj. JSP Maltmill powered @ 300 rpm and batch sparging. Cooler is silver in color, therefore good for an extra 5% over blue. 
What??? Of course color matters! Blue coolers get higher efficiency…didn’t you get the memo??
I suppose a lot of people already know, but I use a 48 qt. Rubbermaid cooler with a hose braid. It’s been in use for 10 years and 358 batches without modifications.
After reading all these posts I have a bit of mash tun envy. ;D
I have a 5 gallon Rubbermaid cooler with a stainless false bottom. It works great but only holds about 14 lb of grain. It’s usually not a big deal since most of my beers are in the 1.045 to 1.060 range. Anything over that, I have to suppliment with extract. I may go up to a 10 gallon some day, but for now it works great.
once you go big…
you start getting FAT ;D
Since this is the AHA, and all, my mash tun is a sort of a Denny Conn-ized ZAPAP:
a 6-gallon plastic bucket with a hose braid, instead of the original ZAPAP’s false- bottom approach.
I insulate it with whatever is convenient at mash-in - works great, actually.
I owe a lot of brewing enjoyment to that setup, and those who inspired it.
I use a 5 gallon Rubbermaid round drink cooler with a copper pipe manifold in the bottom.
I use a 20 gal ss pot with a false bottom. I wraped a piece of water heater insulation around it holds the temp much better.
5 gallon round cooler
(it was free)
with SS false bottom
60qt igloo ice cube dennyized
I still have my ZapPap-I used mine for about 4 years before I upgraded to a converted keg system.
I used a 10 gallon Coleman Cooler with a domed false bottom for a few years that worked great. Much better than the rectangular cooler with manifold I started with. Now I have a sculpture that uses 15 gallon stainless kegs.
15 gallon polarware with false bottom and dial thermometer or 10 gallon rubbermaid cooler with phils phalse bottom (which I would recommend for newer all grain brewers).
A crappy coleman cooler with a crappy slotted coil in an Armstrong System. Of course if I am making more than one mash at the time it could be an old bottling bucket with a drilled coil, or a red cooler (forget the brand) with a drilled coil. Still use the cinder blocks, but now use some plastic sawhorses and an old piece of counter top.
Sawhorses are AHA certified! I have an old door for my platform. I need to think up a sculpture.
same exact here, cept with a bazooka screen.