Out of things I know about, it has to be Leicester IMO. It's harder than Greece or Denmark winning the Euros. Those tournaments favour defensive teams, and- like the CL- it's far less games to get through. Also, a lot of top players are knackered in the summer, so you get surprises. We've seen other teams who play in a similar way do well even if they haven't gone on to win it.
I actually hate them, but Leicester winning it, even though many things were in their favour and many teams had inexplicably bad years, is simply insane in this day and age. It's one of my biggest regrets that our young side weren't ready enough to win it that year- though I still contend that the side that really missed out was Woolwich, who had the experience and the players to take advantage but didn't do it.
I don't fully know the context with Kaiserslautern, Montpellier etc so I can't really judge if these were comparable.