Herts Archives and Library Service (HALS) http://www.hertsdirect.org/libsleisure/heritage1/HALS/ Holds all surviving parish records for Hertfordshire. HALS does not offer these for sale on microfiche, only microfilm, so very few people own them. A lot of parishes have been indexed by HALS and all Herts marriages up to 1837 have been indexed. (Allen Index) This has been computerised and extended by Brian Gravestock and some marriages after 1837 have also been indexed.
Most of Hertfordshire's main libraries have Local Studies Rooms. As well as containing lots of interesting local history books, they also contain microfilm of the parish records for that area.
Herts Family History Society The HFHS has indexed a large proportion of Herts burials which are available online – pay to view at the Federation of Family History Societies website. http://www.familyhistoryonline.net/database/index.shtml