A few days ago I started noticing a crackle + hiss in my headphones. Thinking they were broken I tried them out on my laptop only to realize it was the headphone jack on the front of the G5 (the same G5 I dropped down some stairs).
I researched a few of the USB sound cards from the usual suspects (Griffin, Creative) only to decide on something put out by a company that received nothing but high-praise from everyone who had dealt with them. HeadRoom (located at headphone.com) seemed to be selling exactly what I wanted, though for a bit more than I had intended on paying.
I just received the Total BitHead today and it's worth every penny. It set up right out of the box, came with the necessary USB cable, and delivered a full and dynamic (I realize this sounds like a cliché-filled, paid review) sound. Before if I wanted to hear the all the bits of music I had to just turn the volume up, now it seems like everything is accented and more real sounding.
I haven't ran it through my iPod Nano, and I probably won't be carrying it around that much considering it's slightly too big for my pockets, but it's nice to have the option, especially for my laptop.
Totally worth buying. I am not a golden-eared, audio-phile who goes all wobbly at the idea of a glass-plate turntable, but I know what sounds good, and this sounds great.