Monkey in the middle is great for three people! (At least two of three will enjoy it).
But really a good game is modern roshambo that I have not had the luxery of participating in such an excellent and highly recommended activity. It's where two or more guys hit eachother in the groin until the participants give up or fall to the ground, last person standing is the victor. (NOTE: If you plan on having kids you probably shouldn't particpate in such a game on multiple occasions.
Three team volleyball. Set the court up as a circle. Divide in into thirds with some sort of improvised net (if it is solid and a little higher than regulation it is better, because you can't see where the ball is). Same rules apply as for regular volleyball, but you can only hit the ball twice.