The three main base data sources for climate data

From "Watts up with That":

The three global temperature records are usually called CRU, GISS, and GHCN. Both GISS and CRU, however, get almost all of their raw data from GHCN. All three produce very similar global historical temperature records from the raw data.

We know that CRU weren't impressed with GISS due to urban heat island effect not being taken properly into account ( is this the case ? Need to check ).

So that leaves only one thread left - GHCN.

Time to look them over.....