I like my tea in large mugs, there are very few well designed mugs which would hold more than 350 ml (~12 oz) of water. I know most people don't mind or prefer their hot drinks in smaller mugs.
Also additional challenge is that majority of shops online actually don't tell you how big their mugs are, and I stopped looking having spent few evenings trawling internet a couple of years ago.
The best design of a mug I own (as in how it is engineered so it holds properly in my small hand) is a 450 ml mug from Starbucks. I feel that Starbucks had them designed by some professional industrial designer as they just feel right in my hand. I would however prefer a no brand look.
Do you know any other places which produce good quality, no brand mugs? Do you have any favourites?