Drake Software
Barney Tyrwhitt-Drake is an active genealogist who regularly posts on the BUCKS-L, SOG-UK-L and GENBRIT lists. He founded Drake Software Associates - which produces a number of excellent CD's covering areas adjacent to Hertfordshire, although he has now sold the company:-
Pigot's 1830 Directory for Berkshire, Buckinghamshire & Oxfordshire - a searchable data base linked to facsimile images of the directory.
MACH (Mapping and Analysis of Census Households)
Buckinghamshire 1881
Bedfordshire 1881
Buckinghamshire 1891
These not only provide good searching facilities for the census returns, but will also produce such goodies as distribution maps by parish - or by county within the British Isles. The 1881 data is an edited version of the LDS 1881 census data, while the 1891 data was indexed by the Bucks Genealogical Society.

Map showing the distribution of the surname Monk in Buckinghamshire.
See MONK, Hemel
Hempstead, 19th century