Where can I find free spatio-temporal dataset for download?
If you have R and the spacetime package then you are only data(package="spacetime") away from a list of space-time data sets bundled with the package:

Data sets in package ‘spacetime’:

DE_NUTS1 (air)          Air quality data, rural background PM10 in
                        Germany, daily averages 1998-2009
fires                   Northern Los Angeles County Fires
rural (air)             Air quality data, rural background PM10 in
                        Germany, daily averages 1998-2009


then for example:

&gt; data(fires)
&gt; str(fires)
'data.frame':   313 obs. of  3 variables:
 $ Time: int  5863 5870 6017 6018 6034 6060 6176 6364 6366 6372 ...
 $ X   : num  63.9 64.3 64.1 64 64.4 ...
 $ Y   : num  19.4 20.1 19.7 19.8 20.3 ...