Home Depot has Green Fiber cellulose insulation bags for $5.39 each, covering ~40 sq ft per bag at an R-19 rated thickness. Get 20 bags or more and get a free blower rental. My local store stated it was a 7-day rental.
GreenFiber Natural Fiber Blow-In Insulation - 40 Sq. Ft, - INS551LD at The Home Depot
This material qualified for the 30% Federal Tax rebate, up to $1500 total (through entire 2009-2010 program) max, not to exceed your total federal tax liability (aka non-refundable tax credit). Here is the guarantee paper needed from Green Fiber when filing your tax rebate:
http://greenfiber.com/_assets/PDFs/PM-6.3-154.pdf
Tax Rebate homepage:
Federal Tax Credits for Energy Efficiency : ENERGY STAR
Cellulose is generally more fire retardant, more eco friendly, and much more pleasant and efficient to install. It's not with its cons, though. It's slightly more expensive per square foot per R-value, but only by a hair without factoring additional needs for fiberglass insulation installation. I've heard from some folks that vertical installs of cellulose suffer more settling (thus greater R-Value loss) - not sure how accurate that is, though.
Cellulose insulation vs fiberglass insulation cellulose versus fiberglass - Google Search
40'² @ R-19 Green Fiber Cellulose Insulation - $5.39 ea, free blower with 20+ 
