Above you can preview any of the tracks from the official GTAIV albums. I won't be releasing that music since it's sold, but I will be releasing everything else, such as the commercials and talk radio.
 
Below you'll find the radio montages from the official website, each one a preview of an entire album's worth of material. That should give you a good idea how much effort Rockstar put into just the radio portion of the game.

LibertyCityRadio.net - Vol. A   LibertyCityRadio.net - Vol. B