Sam,
Are you looking to build a string or buy a string? What type of bow is it for? Is the bow made to handle the new modern string material like fast flight and such? For a bow made to handle modern string material, I prefer dynaflight97. It is low creep, good speed, and is quieter than some other fast flight material, IMHO. If your bow isn't made to handle new material than you can't go wrong with good old dacron B-50 or B-500. There are alot of other materials out there you can make strings out of, gut, silk, hemp, etc. Give us a little more info on what you are looking for.