Marwin manufactures a line of wooden and aluminum attic stairs. They offer a couple of lines of each with different duty ratings. They also offer many different lengths and rough opening configurations for both styles. Energy saving options in aluminum and wood as well as fire retardant stair products. Marwin also sell several other lines which you can see at their site.
Rainbow Attic Stair is the Rolls-Royce of attic access. Heavy weight capacities. telescoping ladders with a powder-coat finish. Excellent insulation values. Superior construction. Even remote control units. Loft access units. Self-adjusting. Folding units up to 15' ceiling heights and 570 lb. capacities.