For architectural gems with real ale see Peverill of the Peak, The Briton's Protection, Mr Thomas' Chop House and there are a couple of very thin bars, one is called the Circus I think but the one next door is great too.
For more modern/craft type places, also with real ale you can't do better than stroll around the Northern Quarter - Odd Bar, 37 Thomas Street - minimalistic place, more like a coffee shop but with barrels on counter, Bar Frindge - excellent Belgian style place and many more. Also there is Hare & Hounds, only one real ale but an old school pub that had free sausage rolls when I was there a few weeks ago.