Lowenbrau relatively easy to find in London - one of the bars at London Bridge stocks it. Have also seen Oranjeboom on tap as well - now that's something I thought had disappeared for good.
I have drunk all of the below in my time, and some were my drink of choice for a while (no, not rum & pep):-
Rum & pep
Rum & black
Port & lemon
Holsten Pils & barley wine
Light & bitter / pale & bitter
Brown-bitter
Brown & mild
Black & tan
Guinness & black
Mickey Mouse / Chinese / golden...