There are few things in this world as annoying as wobbly tables. They rank right up there with mosquitos. However, if you're table is in particularly bad shape then it might need a solution like this. You can use a wine cork to permanently fix any table that might have a case of the wobbles. Just take the cork and measure it against the table leg and ground, marking the space with a pencil.
Next, cut off the extra length and attach it to the bottom of the table leg. You can do this using glue or a screw, depending on what you have lying around.