TS - fast and brutal
CV - A total package and a great casual player
IJ - Probably one of the best theme integrations and plenty to do. Plus, widebody.
WH2O - Easy player, but challenging to stack modes for advanced players
LOTR - long epic game for when you want to just play a couple real long ones.
TX Sector or Robowar - I like those 80b's just for a changeup and these have awesome midi tracks!