SORT (the Society of Revisionist Typographers) are based at Cockpit Arts Studios, Holborn. Fantastically handlebar moustache-esque, SORT make a range of cards and notebooks available through their Etsy webstore, and also wedding stationery (email them for a catalogue).
The New North Press based in Hoxton produces some lovely prints like this one of the Oranges and Lemons nursery rhyme - for the cockney sparrar in you.
Also check out Papermash which has a range of cards, notelets, and gift tags - when asked to 'Bring a Bottle' these tags are a good finishing touch. Nothing like a bit of honesty, eh?