Hopefully there's the appetite for this thread.
I guess we all live in hope of finding discounted massage via Groupon, Wowcher etc that maybe offers a bit more.
Rather than just post where we got lucky I was thinking it would be useful to post where the massage was legit too.
I'll start it off:
Siam Body & Soul - Carlton Street NW1 - Near Kings Cross - very good massage but 100% legit. The place seems to have European masseurs rather than Thai (as the shop name suggests), but was still a very good experience.