beer & lemonade = shandy (bitter shandy)
lager & lemonade = lager shandy
beer & Guinness = black & tan
lager & cider = snakebite
champagne & Guinness = black velvet
champagne & orange juice = buck's fizz (I think)

"and black" means with a dash of blackcurrant, e.g. cider and black

"top" means a splash of lemonade (or possibly lime, I don't know which -- not something I do personally (yeuch) --), e.g. lager top

HISTORICAL NOTE
gin & port = flesh & blood (I found this in Georgette Heyer: it's remarkably good)