Geo.me Global Climate Data
Earlier this month the UK Met Office released a data set showing the monthly average temperature values for over 1,500 land stations, in some cases going back over 300 years. Geo.me has produced a Google Map mashup that allows you to view the data for all of the 1,500 land stations around the world.
If you click on any of the land station map markers on the map you can view data, including the location, nearby stations, current weather and a plot of monthly average temperatures.
Geo.me have also produced a Climate Trends Google Map that illustrates the average temperature data for a location for a selected month and year. Controls above the map allow the user to to change the time period and the display properties of the map.