Well when it comes to beer I don't care about ascetics, I bought a 52 qt Coleman marine cooler. It was inexpensive, around $35. (notice I said inexpensive, not cheap, when it comes to brewing equipment price is important, but not paramount) It is a good size for the 5 gallon batches I run right now. I batch spare so it holds my strike water and grain bill (typically 9-11 lbs) with plenty of room for stirring and a decent grain bed. It has plenty of room for 'big beers' and larger batches if I decide to run them.
I agonized over my mash tun(cooler) purchase for 2 or 3 weeks, I almost bought a round drink cooler, but am very happy with the purchase I made and expect to be using this tun for years to come.