If you have the money, the best lens that I have come across is the L 70-200mm 2.8f IS. Its a little $$$, but I bought one from B and H in New York, and its the best lens I have purchased. Great for portraits, long shots, wildlife... As for my primary lens (with the 300D and 10D) is the L 17-40mm 4f. Real solid lens, and a little more wide angle than the one that comes with the 300d. Thats my 2 cents worth.