Originally posted by: ayabe
Well how deep are we talking?
If it's a clearcoat only scratch and you want something that works well by hand, I can't recommend Meguier's Scratch-X enough.
It will take several applications and some elbow work but I've used this extensively on my black Subie with great results. It's impossible to mess up practically as long as you use the right applicator.
Deeper scratches will need to be machine polished out, which you may or may not feel comfortable doing yourself.
If it's down to the metal or primer, then you need touch up paint or will have to repaint the panel.
Any pictures? Can you feel the scratch if you drag your fingernail over it?