I'd second Old Spike and Volcano, 40 Martell Road, Norwood. It's a pleasant stroll from East Dulwich. I'm not sure if they still offer you a free coffee if you buy more than £15 (I think, from memory) of coffee beans, pods etc. in store.
I'd also like to recommend Tony from Only Flues and Hoses. Not only has he chosen a genius name for a plumbing business based in South London, he also came out on a Saturday morning to fix a leaking pipe in my bathroom.
His service was prompt and professional. He diagnosed the problem and fixed it quickly, which is a weight off my mind.