I'm using a new toy in the GT. It's not great - but it's OK. It's a USB memory stick FM transmitter - so I've got a gig of albums, everything from the Yellow Jackets through to Steely Dan and it just plugs straight into the cigar lighter. An all in one unit.
http://www.the-gadgeteer.com/review/mp_308_car_usb_fm_transmitter_review
Don't buy one from the above link - you can find them for about $20.
Now this ain't exactly high fidelity and I have some understanding of the subject - but it's OK for having all your tunes at FM radio quality.
PS obviously don't use it with a card reader! A little USB stick is much neater.