Hampshire Genealogical Society have the Hampshire 1891 census index on CDROM and the Hampshire 1851 census index as books and microfiche. The 1891 index and (so far) about 20% of the 1851 census are available in the FFHS pay-per-view site Family History Online
1881 U.K. census index online in FamilySearch From the home page choose "search", it is one of the free databases available. It is also available on CDROM. From FamilySearch home page choose Order/Download products, search for "British Census" or "1881". The index is available in Family History Centres of the Church of Jesus Christ of Latter-Day Saints, from all their distribution centres, and in many other libraries.
1901 Census Online for England and Wales is available from The National Archives (Public Record Office). Free search, pay per view for transcript and facsimiles.
1871 census for Southampton and neighbouring parishes has been produced by Southampton City Libraries Family History Club and published on CDROM in 2004 by Southampton City Council - contact Special Collections Library, Southampton Reference Library, Civic Centre, Southampton SO14 7LW; phone 023 8083 2205; email local.studies[at]southampton.gov[dot]uk.