Go to Pandora.com In the search box type "90's" Then choose the genre you want. Alternative, rock, country. You can even choose to play the top hits from a specific year.
Pandora uses your feedback to improve the music they play for you. If there's a song you don't like you can thumbs down it and it won't play again. If there's songs you do like you thumbs up them and it will play the more often along with other music that is similar.