critical essay on T.S Eliot

we have just started studying T.S Eliot and I am really fascinated by him and by his works (we have already read "The Love Song of J.Alfred Prufrock, which I loved, and we are currently reading The Waste Land). I like his poems first because of the way they sound, but then I have some difficulties in understanding their meaning (well, to tell the truth, my personal interpretation does not always get along with that given by my teacher:D )...so, I was just wondering whether you could suggest some critical essay on T.S Eliot by someone expert in the field (the book my teacher uses as a guide often can't answer our questions...i.e: in The Waste Land, verse 25, "There is shadow under this red rock"; why is the rock red?).
Thank you a lot!