Seconded on the Bree Louise. Excellent beers, including oddballs like weirdly herbal (but delicious) flat, thin stouts poured, as mentioned, by gravity. Good proper cloudy cider on hand-pump too, if that's your bag. I may or may not have eaten a half-decent pie there at some point, can't quite recall - there are signs all over the place bigging them up, at any rate. Nice to sit outside when it's sunny. I've found the staff can exhibit indifferent levels of politeness and/or command of English, though it's not consistently a severe problem.
Surely a contender for one of the most oddly named pubs in London? I mean, "Bree" - is the publican called Butterbur?
Edit: on the point about big brewers, I've been spending a good deal of time in Oxford since the start of the year and while the city's obviously got loads of great pubs, it's noticeable how many of them - seems like a full half of them at times - are run by the dreaded GK (based in fucking Bury St. Edmunds, I mean hello??) and many of the others are owned by one of the two big London brewers. It's a real shame, I mean surely Oxford of all places should be able to support a good number of free houses? Or at least houses tied to one of the smaller, more local breweries - I can't think of any in or just outside the town itself off the top of my head but casting the net a bit wider in the West Country there's Arkell's in Swindon and Hop Back in Salisbury, for a start...