Warning: This answer is outdated. As of writing this warning (6.10.2013) the kernel-ppa used here is no longer updated. Please disregard this answer.
Small note: Installing anything but the official standard kernel for your system is not recommended. It might be unstable or buggy. Now to the topic:
This adds the daily build of ubuntu kernel (not mainline):
sudo apt-add-repository ppa:kernel-ppa/ppa
sudo apt-get update
sudo apt-get install PACKAGENAME
You can do the same with Software Center or Synaptic using the menu item "Repositories". From there you'll need to click through some self explanatory stuff.
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