Soccer tennis! This game is a ton of fun.
My friends and I made up our own version of rules before we knew anyone else played it, and I think they work better for players who aren't really good.
Use a regular singles tennis court. You can limit this to just the half closest to the net if you have 2v2 or 1v1 (this is normally played 3v3 but anywhere from 1 to 4 per side works) and/or are just starting. Serve from behind the middle lines by bouncing the ball then hitting with your foot. Unlimited touches are allowed per team and player, and any body part is legal besides hands/arms. One bounce is allowed per side before contact is made, after that if it hits the ground it's the other team's point, like in tennis. We use volleyball scoring (only score on serve), and call it stennis.
http://soccertennis.org/ is a link to an organization with somewhat different rules and a video on their homepage.