My friend has this Hoover that looks like one of those professional grade vacuums (you know big barrel for the waste depository and a hose that can suck the hair from your head) that has an option to blow air out also. Honestly it's like a leaf blower you can use inside your house and it works wonders on computer dust. Just make sure you have nothing that can detach and potentially slam into some part (ie CCFLs, loose screws, even flimsy PCI cards that can blow over and crack). But when I don't have access to that, canned air while your PC is outside works well. Hope NASA doesn't fire me now.