It was on my earlier post.
If you have Ancestry, when you do a Person search for a particular census, and are presented with a list of names. Click on "view record" on the left of the name you are interested in, instead of "." on the right.
The "Source Citation" at the bottom of the page includes all the info required for others to find the person.
In 1841 census, the important bits are piece, book, folio and page.
In 1851 -1901 census, the important bits are piece, folio and page.
As an aside, you can search street names for 1841-1871 census, at the Your Archives section of the National Archives. A work in progress, 1881 and 1891 to follow. Gives the reference numbers. Sometimes comes in handy cross checking birth/marriage cert details etc against the nearest census. You get house/street searches for 1841-1901 census if you have a subscription with thegenealogist, but its something missing from Ancestry.
http://yourarchives.nationalarchives.gov.uk/index.php?title=Your_Archives:Historical_Streets_ProjectAlan.