One of the main record collections I have used at ancestry.com.au are the Census returns for the United Kingdom. The record collections include:
1881 Channel Islands Census FREE INDEX
1881 England Census FREE INDEX
1881 Isle of Man Census FREE INDEX
1881 Wales Census FREE INDEX
1911 Channel Islands Census Summary Books
1911 England Census Summary Books
1911 Isle of Man Census Summary Books
1911 Wales Census Summary Books FREE
Ancestry also has the following census collections for Ireland
Ireland, Tithe Applotment Books, 1823-1837