A while ago MacUpdate put together a bundle of Mac software. Being a compulsive buyer, I bought it. I can't remember which program got me excited about the bundle, but I came away with a lot of software I'm really enjoying. The program I'm enjoying most, however, is called SRS iWOW for iTunes. It's a sound enhancement plugin for iTunes that makes the laptop speakers on my MacBook Pro sound roughly 6.73 times better than they did before. The plugin also includes presets for listening to headphones or for when your computer is hooked up to your stereo at home. It doesn't work over AirPort Express (damn!) but the effect it has to music playing out of your laptop speakers or headphones still makes it worth the purchase price of $19.99 SO worth it. I think they even have a PC version (like you care!).

You can get it here.