I wanted a radio unit also. I went ahead and bought the Shark system about a month ago, installed it, and found the the sound of the radio always sounding slightly off frequency. I found a used iPod nano (5th gen) that has an FM radio in it, but it seemed to not pick up station very far from the transmitter. The two add on radios I've been researching are the Jensen HD910 and the CycleSounds Rockbox. The Jensen is weather-proof, a larger unit,a built in equaliser,switchable Euro or American AM frequency spread, and a speaker and line level output, as well as a 3.5 mm aux input. It also has a weather radio(works only in the US) and a true antenna connector. I've found it on eBay for about $150 but retail outlets are $175-$250. I couldn't find a lot of real info on the Rockbox, so I called the owner of the company. He told a whole lot of info,and here are some of the highlights: FM radio only((sorry if you want AM), time and temp display, tone and balance controls, able read music directly from the USB port and display limited info from that source as well as charge external USB toys(phones and such), an aux 3.5 mm input, a 3.5 mm output for your installed amp,weather-proof, and a smaller foot print.The owner also says that you can add an external antenna. The retail price is $299, but a web search found it for $244.50. Both radios have at least 12 presets to store your favorite stations.
The Rockbox has gotten rave reviews, so I've decided to go with the Rockbox, but will not get it until Christmas as a gift from my wife.
Dennis