Here are some ballpark sway bar sizes to get you going. It is important to have the right size rear bar in relation to the front so that handling on the car stays as neutral as possible.
<table border=1><tr><td>Front bar</TD><TD>Rear bar </TD></TR><TR><TD>7/8ths</TD><TD>11/16ths </TD></TR><TR><TD>15/16ths</TD><TD>3/4 </TD></TR><TR><TD>1</TD><TD>7/8ths </TD></TR><TR><TD>1 1/8th</TD><TD>15/16ths </TD></TR><TR><TD>1 1/4</TD><TD>1</td></tr></table>
Remember these are ballpark. There are many things that effect handling such as engine weight, tyre size, etc.
Here is a table showing how you can fine tune your car to handle correctly.