United States:(National Climatic Data Center). Contains monthly mean temperature and precipitation data that dates back to 1900: Time-Series trend data can be found here. The statistical climate information can be found here.
ENSO SST Anomalies (Select Data): (UCAR) TNI, R 1+2, and R 3.4. Contains data from 1871-Present. Reconstructed (From 1300 to near present). Historic ENSO Anomalies (hadISST) from 1870-Present: Regions 1+2, 3, 3.4, and 4 (ESRL)