If you are looking for inspiration on what music to buy next, I have already sung the praises of The Wire magazine if you wanted to look forward and discover music.
If you wanted to look back, though, you could do worse than checking out this website: www.muzieklijstjes.nl/mojohowtobuy.htm . Yes it's Dutch, but as it collates information which is purely artist names and album titles, all the info is in English.
It lists the top ten albums of the best releases of a certain artist, band, label or genre as voted for by the readers of Mojo magazine. And they are usually pretty spot on.
So, if you wanted to kickstart a John Martyn or Quincy Jones collection, this is for you. I have found these lists invaluable and I hope you do too. Let me know if it helps in any way.