Of course about the best loft insulation is made from recycled newspaper mushed up and blown into the space between the rafters. A bit messy and difficult for the man-in-the-street to find an installer, but it has a higher insulation result and it doesn't take up non-renewable resources like most other forms. I can't remember what's it called off hand, but I found out about through the Centre for Alternative Technology (http://www.cat.org.uk/)

Another good insulation material is sheep's wool.