For raw code speed practice, RufzXP is hard to beat. I'm not sure why anyone would want to limit the number of callsigns, though.
Another excellent resource is LCWO Learn CW Online: http://lcwo.net/
It features callsign training, word training, random code groups, and much more.
Our K9YA Field Day group prefers Morse Runner, because it creates a more realistic contest simulation with QRN, QRM, and lids.
Nothing beats actual on the air operation, though.