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.
The Free Census Project FreeCen aims to provide a "free-to-view" online searchable database of the 19th century UK census returns. See FreeCen Hampshire information page for areas being transcribed, and those completed.
1891 census index from Ancestry - complete for England and Wales - and 1901, 1871 for some counties. Free search, subscription basis to see transcripts and facsimiles
Archive CD Books has published various census facsimiles and place indexes on CDROM. See "Great Britain - census" in their catalogue. Hampshire 1841, 1861, 1871 are in progress.
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.