The Lennox Diemaster Bimetal blades. I use 1/2 inch by 3 tpi for cutting circles. The bi metal blades have M42 HSS for the teeth, which is the metal they use on pallet cutting blades. If you have a local saw shop they may be able to make them for you. They cut longer and straighter than any other blade out there, and if you have a good saw shop, they can be resharpened several times. With a 1/2 inch blade, you can cut a 6 inch circle fairly easily. They come in different thicknesses, and I can't remember the numbers on mine, but I like the thicker ones.
robo hippy