Dynamat or similar sound-deadening material will help. I've also heard of people using some spray-on stuff inside the wheel wells with good effect - don't know how long it lasts.
Do you have a roof rack that you're not using? Removing it will help cut back on wind noise, provided you have a 'fill in' kit like the one my car came with.
I don't know what tire size you have but, in the 235/70/16 size, the quietest ones according to Tire Rack are:
Continental CrossContact LX (8.9, on a 1-10 scale for "noise comfort)$93.00
Goodyear Fortera SilentArmor (9.1)$121.00
On a tighter budget, the Kumho Road Venture HT score a 8.6 for noise, and go for $75.00, and are very well reviewed.
Finally, the Avon Ranger TSE goes for $85, and are too new to have a score, but so far have earned a 'Consumer's Digest Best Buy' and a couple of people have commented on how quiet they are. Made by Cooper.
Or you could just buy a louder stereo.