Jim Carter sells the simplest (HPM544) intake manifold heater kit. It will work fine with a standard intake manifold.

Some people use water but it is more complicated and the water does not truly circulate unless the intake manifold (and plate) are set up for circulation throughout the intake manifold.

Clifford intakes and Offenhauser intakes will circulate water with the correct heat plate kit (Tom Langdon's kit (that I bought this past summer) will not circulate properly with these two types of water-heated intakes).