[pushkins]

Gypsum is about your best bet unless you want to get into the world of drainage. With gypsum your trying to help the clay break up enough to let the water percolate through the soil, with drainage like French drains etc... your allowing the water to collect and be moved away. A wise man once told me, "NEVER try to beat water (cause you won't), rather work with it", water is essentially lazy it wants the path of least resistance, that's why drainage sometimes is the best and most cost effective answer.

Just to show what lengths some people have to go :

Saw a guy once, he had a lot of clay based water problems that he was unable to solve with conventional drainage because of grading and house positioning reasons, he had a soil drill sample done and found about 8' down under the clay was a very good drainage level of sand, he had thirty holes drilled 6" diameter 16 feet deep then filled with drainage gravel then he topsoiled the entire area with a sand based topsoil to 6" deep then re grassed the area. The topsoil allowed the water to seep down to the clay, the water then filtered into the 6" holes, through the rock and into the sandy layer under the clay, problem solved. It cost him $15K to do this and it was part of a much grander landscaping project but it worked.