I have always been a real ale/microbrew fan, so I guess I'm not the most partial. Sometimes, if we go to the pub and all they have is "normal" lager, I just drink soda.
Some of my favorite nationally available ones are Badger beers (esp. Golden Glory and Blandford Fly), Hobgoblin, Pedigree, Black Sheep, Fursty Ferret, Double Maxim, 6X, Deuchar's IPA, Discovery...the list goes on. If you get a chance to go to a beer festival, it can be very interesting to taste some of the local brews. And you should try a proper cider and perry (not just Strongbow!), but be careful--they can make you really ill if you have too much. Old Rosie is a good one, I forget who makes it, but it's quite strong.
And then there's Newcastle Brown, but I'm not sure if that really counts as real ale. Pretty nice, though.