We have 2 cats.
One brings me the occasional mouse or bird, he has brought me a live blackbird and live mouse before. Thankfully we don't have a catflap anymore, so the live presents have to stay outside. He does like throwing them at the patio windows though.
My other cat has only ever brought me a bag of mince, and a raw pork chop. I'm not sure if that makes him very stupid or very clever.
Unchief - AugustusRookWhooosh is right. Your cats present is its way of contributing to the household. If you get annoyed at them they're likely to bring you something bigger.
A friend of mine was very upset about having to move house, she spent the whole week crying. Over the course of a that week her cat brought her a mouse, a small bird, a bigger bird, a rabbit, and on the final day the cat went and ripped the front of the neighbours rabbit hutch to bring my friend the injured hare the neighbours kids had been nursing back to health!
Call them vicious little murderers, but make sure you do it in a nice affectionate tone of voice.