new lens?

Okay photography friends, I need your help! I think it is time for me to start saving for a new lens, but I don't know what I want to get. I have a Canon Ultrasonic 28-200mm 3.5-5.6 and a Canon 50mm 1.8. I love, love, LOVE my 50 mm lens! I also like the versatility of my zoom lens, but to be honest, I'm not always crazy about the quality of the photos when I use it.

So what is your favorite lens? What should I add next? A better zoom lens? Another fixed lens? What is on your wish list?