fianchetto,
The Chess Assistant site has a demo download of their endgame trainer, you could start there.  If you like it I think it cost about $30 US.  Also the Universiyy of Pittsburg Archive of games  has a couple of endgame collections.  Simply go into the archive and look in the index. It's free, but the positions are computer generated which means some are not really challenging they just happen to meet the search criteria for say B+PvsK.
Of course if you have chessbase/chess assistant you could do a material search of a large base to find endgame positions as well.
Hope this helps,