Japan, Finland, Norway, Sweden: the richest 20% are 3-4 times richer than the poorest 20%. In the UK it's 7.9% and 8.5% for the US. Note that the former countries are richer, happier, calmer, and more equal. The differences would be even more extreme if we took the top and bottom 10%. In the US, average wages have actually decreased since the 1970s, while the rich have become massively richer.
How many members of Congress are millionaires? Almost all of them. 22 of the UK's 28-strong government Cabinet are multimillionaires: that's why you won't be seeing equality any time soon.
The US is off the scale for crime, infant mortality, murder, mental illness, teenage births, imprisonment and addiction (with the UK nearby) - the more equal countries, though relatively poorer, are right down on the scale. It's not average income - it's relative, or how the cash is distributed. The USA is hugely rich - but still locks up huge numbers of people (mostly black) and abandons millions to charitable healthcare and poor education because they're ideologically opposed to governments intervening in peoples' lives.
Here's an interesting one: in more unequal countries, people distrust each other more - only 15-25% of Americans and British trust their compatriots, whereas 65-70% of the Scandinavians trust each other, leading to stronger communities and less social decay. The same is true of the US states: Mississipians, Alabamans and Arkansans distrust each other (they also go to church more, vote Republican more and shoot each other more, which goes to show that liberals and lefties are just nicer people).