Here is a selection of sites you may find useful or interesting. 

Nearby societies and organisations:

East Herts Geology Club 
Bedfordshire Geology Group
Bucks Earth Heritage Group
GeoSuffolk – based at Ipswich Museum
Geological Society of Norfolk
East Midlands Geological Society - based at Nottingham
Essex RIGS Group
Hertfordshire Natural History Society

GeoEast  (the East of England geodiversity partnership) -  umbrella organisation covering Bedfordshire, Cambridgeshire, Essex, Hertfordshire, Norfolk and Suffolk. HGS is one of their partners.   Their 'Geodiversity' page gives an interesting and varied introduction to the region.

National organisations:

The Geologists Association – lectures and field trips throughout the year
Rockwatch - the junior club of the Geologists Association
Geological Society – includes current news items relating to geology
Open University Geological Society Lectures and field trips – not just for OU students!
British Geological Survey – maps and a huge array of other resources.  E.g. interactive version of UK 1:625000 scale geological map that you can download and view using Google Earth.

For newcomers to Geology: 
Some commercial sites offer a range of accessible information for beginners, often with an emphasis on fossils.  We mention a couple purely as an example of such resources.

Discovering Fossils - try their 'Locations' and 'Resources' pages
UK Fossils – includes an interactive map of UK fossil hunting locations

Miscellaneous:

Sedgwick Museum, Cambridge Their ‘Links’ page gives a very extensive list of sites under various useful categories – well worth a browse
Thin Sections Atlas - a University of North Carolina site containing an extensive atlas of thin sections of both minerals and rock textures.

And something for those particularly interested in the Quaternary...
UCQPG maps - maps of northern European drainage system over last 3 million years

New:

Hertfordshire RIGS  (page under development)
Puddingstone (page under development)