This is the pollution data set so loved by writers of papers on ridge regression.  Source: McDonald, G.C. and Schwing, R.C. (1973) 'Instabilities of regression estimates relating air pollution to mortality', Technometrics, vol.15, 463-482.

Variables, in order:

PREC   Average annual precipitation in inches
JANT   Average January temperature in degrees F
JULT   Same for July
OVR65  % of 1960 SMSA population aged 65 or older
POPN   Average household size
EDUC   Median school years completed by those over 22
HOUS   % of housing units which are sound & with all facilities
DENS   Population per sq. mile in urbanized areas, 1960
NONW   % non-white population in urbanized areas, 1960
WWDRK  % employed in white collar occupations
POOR   % of families with income < $3000
HC     Relative hydrocarbon pollution potential
NOX    Same for nitric oxides
SO@    Same for sulphur dioxide
HUMID  Annual average % relative humidity at 1pm
MORT   Total age-adjusted mortality rate per 100,000