I'm still fairly new to photography, went out this weekend to gather some texture sample images and haven't really noticed before how much lens distortion I get in my images.

I know how to crop the image and fix slight angle problems for photo references but how do you go about fixing lens curve? Is it just cause I was using a crappy kit lens?

Canon Digital Rebel XT EOS
Lens EFS 18-55mm

Also have a telephoto lens too, but didn't use it today.