I just helped a friend of mine install this in his car:
http://www.shop4tech.com/?go=view_item&id=3992&r=274
It's an FM Modulator that plugs inline with your antenna input. It does the same thing as an FM transmitter does, but it's hard-wired. Audio quality is nearly indistinguishable from CD. The box comes with a switch you can mount on the dash to turn it on and off (since turning it on introduces some static to radio reception). Audio input is in the form of 2 RCA cables, but it comes with a 2-RCA to 1/8" (3.5mm) stereo headphone plug (male) for use on portable music players.
Just wanted to recommend that product to anybody looking for a cheap way to get aux audio in without an FM transmitter or tape adapter.
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Jeff 2005 Jeep Liberty Renegade
4x4, 6spd, Leather, Sunroof, trak-loc, skids/rails, hitch+shackle, hooks, Alpine/iPod, Thule, GPS, CB, Frankenlifted w/ 31" MTRs
Photos Cardomain