This site is a great resource for anyone researching ancestors from Sheffield, Yorkshire, England. With over 800,000 pages of history including the 1841, 1851, 1861, and 1871 census, Sheffield's Master Cutlers Index, (from 1624 to 1925), directories, poll books, marriage records, probate records, land records, burial records and more, there's a good chance you will find something. The Apprentices index is also available. There is also a forum for communicating with people in Sheffield and/or researching Sheffield.
Visit http://www.sheffieldrecordsonline.org.uk/ to try a search.
For historical data about Sheffield itself, check out https://en.wikipedia.org/wiki/Sheffield.
For this and many more online genealogy resources, see the Genealogy Links page.