Disgaea: Hour of Darkness and La Pucelle:Tactics are excellent Tactics RPGs, if you fancy trying one of those.

Multiplayer-wise, Bishi-Bashi Special has to be one of the most addictive party games I've ever played. It's only two player, but some of the mini-games are fantastic. I'd also recommend any of the Worms games (though these would be better bought on PC) or Hogs of War, both amusing little strategy games.