Here's a variation of the 1-on-1 drill known as "corners" where one player stays in one corner and moves his paractice partner side to side. In the standard corners drill, one of the player moves side to side until he tires and then the roles switch allowing the dictating player to move as well. We find the standard drill to be somewhat artificial in that the dictating player's energy level is usually ratcheted back while the other player is moving.
In our version, every 3-4 shots the dictating player yells out "switch!!!!" and the moving player has to direct the shots to the open corner. The dictating player then moves to the open corner from where the game continues. Then, after 2-3-4-5 shots (or even 1), the dictating player yells "switch" again and the moving player directs his shots to the open court. The benefit of this drill is that both of the players are moving and that the moving player is forced to constantly shift the angles of his shots while on the run. The dictating player gets to move as well so this drill is usefull in maintaining a high level of excitement for both players. Furthermore, with both players being forced to move and change the direction of the ball, the drill is a lot more realistic and practical than your standard corners drill.
A second variation of the corners drill is where the moving player (or coach) yells "switch" and the roles change in the middle of the rally. For example, wherever the moving player happens to be when "switch" is called out, that's his corner and the player who was previously dictating the play is now the runner (hitting all of his shots towards that corner. This is a great drill for practicing in a team format where 3-4 courts can perform the same task and the coach's directive ("Switch") controls all the courts at the same time.