What Brewdog do best is low abv and session IPA. Dead Pony Club (3.8% abv) is one of their bestselling beers in the UK. There's no way it tastes remotely like 3.8% - more like 5%. I'd been wondering how on Earth they pulled this off and can see now that it's by using an amazingly high percentage of Caramalt & crystal: 22% altogether. It gives the body that is so often missing in weaker beers. This beer is next on my to-brew list, or some variant of it with whatever hops I have to hand.
I haven't tried Nanny State (0.5% abv) but it came out top in a recent review of alcohol-free beers in the Guardian newspaper. Really unusual recipe with an OG of 1007, lots of speciality & crystal malts, tons of hops, but no base malt. I'm dying to try it, but not sure I would brew - it might be a step too far even for me.