Upgrade 18-55

Hi all,

Would like to know your opinion in a lense to upgrade from my 18-55mm.
I have a 300D but will soon pass to the 30D, 90% of the photos I do are planes,I'm a plane spotter, that's my hobby. I don't give much use to the 18-55, use mostly Canon 70-200 f4L. The small zoom lense is more to static planes, and vacations.
Would like to know a +/- cheap ( not more than 400$) substitute for the 18-55. I read some good reviews on the Sigma 17-70, do you recommend it?

Best regards,
Pedro Becken

Well what about the 18-55 makes you want to upgrade? That makes quite a difference... if you're looking for a constant f/2.8 it gives you a few options whereas if you don't mind about that it opens it up to a few others... I'm guessing you might not use f/2.8 much for taking photos of static planes?

I'm thrilled with my Tammy 17-50.. does an incredible job...

Yeah Jim, i would say 2.8 is not the priority. I talked about the sigma 17-70 because that's +- the range i would like it to have.
About the 18-55, i don't know if age interfiers with it(3 years old), but the quality is not very good, must be the use of the L glass most of the time .