First as samm said, clean it, once a month works for me. Also get dust filters on the intake fans, hopefully you have at least a couple. Those are the simple and cheap approaches to keeping the temp down.
You won't really be able to reduce the overall temperature generated by your machine, however you can disperse the heat more quickly so you won't have to eat more soup, install a couple more big 120 fans, new heatsink for the cpu, et cetera.