Apparently obligatory, every website has a table of useful links, so here is mine..

So you might ask, where are all these races, where do you find them? Well the answer often now is online. Here are the ones that I look at:

Running Diary (UK Races)
Association of International Marathons
Half Marathon List - UK Halfs
Future North East Races (NE England mostly)
UK Results (north West England mostly)
Marathon Runners Diary (International)
Scottish Running Guide (like the name says)
Runners World (the magazine, UK races)
run247 (Running Fitness magazine website, UK races)
Entry central (UK races)
Born 2 Run (UK races)
Parkrun (5km timed training runs)

Off-road race listings I look at:
Northumberland Fell Runners
Scottish Hill Racing
Scottish Hill Runners
Next question you might ask is are there any other sites out there that tell me similar to what you are saying? well here are a few:

Powerof10 . Lists individual runners statistics
ARRS - Association of Road Racing Statisticians A group probably with a sense of humour but focussed on the fastest rather than you or I

Running USA. More like what I am trying to tell you here. US based and tells you loads about their races and statistics from over there.

AIMS Statistics (Association of International Marathons and Distance Races).
Statistics about marathon racing, the Marathon times through the years might be interesting - the more time that goes by the faster the winners get.. which means that the average time for the average runner is likely to get quicker too.

Temperature and race times. A curious thought that perhaps we in the UK don't worry about too much, but do we go slower with temperature?

US Half marathon average finishing times by age

Average finishing for 1 race in the UK over the years - so you can get an indication how finishers time change over the years a bit about Haile Gebrselassie world records

World Masters Athletics. These have 2 interesting things for this website. They have a list of world records which is used for "age grading" and also a list of world record holders - the fastest runners there are.