I need LARGE data sets for testing the Dijkstra's Algorithm which I implemented
 

Google gave me this: http://kdd.ics.uci.edu/summary.data.application.html

That seems to be a dedicated site for the data sets, but couldn't find anything there for the Route finding algos.

Could you perhaps generate them with your own programme, then apply the Floyd-Warshall algorithm to check your implementation's results? I guess it depends on how large your 'large' datasets need to be... Floyd-Warshall's O(n^3), if I remember correctly, so it might be too slow for your requirements.

you want something large
i am working with these currently
http://imbrium.mit.edu/DATA/LOLA_GDR/CYLINDRICAL/IMG
the 144 LDEM_1024_ ????.img 900 meg each
the lola "Lunar Orbiter Laser Altimeter" data set