Mineral wool insulation
Mineral wool insulation, like the kind made by Roxul and CertainTeed, is much better than regular fiberglass insulation, as it won't deform if (when, inevitably) it gets wet. It's also much healthier than Icynene or Polyurethane spray-in foam insulation, as it doesn't off-gas. And although there is some controversy as to how safe spray foam insulation is after it cures, there are many reported instances where people develop (or exacerbate) chemical sensitivities after they have moved into a home that was insulated using spray foam.
The safer (and just as effective in creating an energy efficient home) option is mineral 'rock' wool. You can even get a version that is made to both insulate AND provide sound-proofing: great for the rooms where a teenage drummer may once live. :-)