Haus der 111 Biere (update: closed in 2006) iswas indeed an extremely scary place. Like most people, I've only been there once.
It is a great shame that the only pub in Munich that has an interesting selection of beer is otherwise so uninviting. Even the Irish pubs, which are not tied to a particular brewery, all serve the same (bog-)standard beers, although the Twisted Bavarian did have some washed-up bottles of Sierra Nevada for a while.
With regards to shops, about the only place that stocks any foreign beer at all is Hertie, although their always-limited selection has progressively dwindled even further and I'm not sure there's very much left of interest at all. A few pseudo-foreign lagers brewed in Hamburg are still on sale, but the British and Belgian ales are almost all gone, and there were never any American brews there apart from A-B stuff. Pomeroy & Winterbottom stock (at least used to) the excellent Old Peculier, and they can order you a case (12 bottles I believe) of many British ales, but no mixed cases. Nothing from Belguim though, presumably.
Other than that, you would have to order from an online company (hence my question above), and pay the high international delivery charges. Or go visit the places yourself! British beer in particular tastes soooo much better from the barrel.
Related topic: Specialist beer shops for non-German beers - Where to buy British, US, and other foreign beer