Have just had the Stanley ones arrive a few days ago - see link below from Cod I think. They are the big ones, only £5.99 plus £2.95 p&p.
My kids love them. They were so fed up of sandwiches and now love taking their hot spaghetti and beans etc. The food is always hot at lunchtime they tell me.
So glad this thread was started. I would never have thought of this otherwise and they've been a big hit, especially when we had that frosty weather. My 2 said the other kids at school were jealous of their hot dinners.