beecherheather, welcome to the forum!
while most people will recommend the lenses they have and love i would like to ask a few questions first.
why do you think you need a new lens?
what's wrong with your existing lenses?
what are you trying to accomplish by acquiring a new lens?
what's your budget?
if you have just money burning a hole in your pocket feel free to PM me about the 50mm i have for sale
hehehe