My quest for a good'un has led me through mires of cheesy slogans, odd shapes and boring designs, but I think I've found some winners.
First up, the legendary Wild and Wolf make some really good ones. One of my absolute faves is this world map hip flask for £19.95: I would take it to far-away places and use it to plot my adventures whilst tipsy.
Ted Baker's stag hip flask is all atmospheric and eery. You could drink from it at a picnic on some windswept moors and its contents would warm you up - pretty and functional. It's £25 from The Hollies Farm Shop.
Wild and Wolf also had a hand in designing the Wanderlust hip flask. I don't really know where to start in listing all of the awesome: stripes, flowers, zebras, flamingoes and a parrot! I can even see a cheeky giraffe in the top corner. Although I'm not sure this would be appropriate drinking-material for a trip to the zoo. It's £20 from Amara.