The Ubuntu kernel guys have released an official build of the 2.6.31 Linux Kernel.
The .deb files should work with both Ubuntu and Debian and distributions based on one of the two.

The included kernel files have been compiled using the generic ubuntu configuration.
Note: nVIDIA ForceWare drivers are automaticly installed using DKMS (which is included in Ubuntu 8.10 and higher including 9.04 and 9.10)

The required files can be found at http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.31.5/

Installation Guide

1. Download linux-headers-2.6.31_all.deb
2. Download your kernel headers package;
   I386: linux-headers-2.6.31-i386.deb
   AMD64: linux-headers-2.6.31-amd64.deb
3. Download your kernel compile;
   I386: linux-image-2.6.31-i386.deb
   AMD64: linux-image-2.6.31-amd64.deb
4. Install the files in the following order:
   1. linux-headers-2.6.31_all.deb
   2. I386: linux-headers-2.6.31-i386.deb or AMD64: linux-headers-2.6.31-amd64.deb
   3. I386: linux-image-2.6.31-i386.deb or AMD64: linux-image-2.6.31-amd64.deb
5. In the terminal run:
   sudo update-grub
6. Reboot and select the kernel from the bootloader menu

For those who want to do their “own” compiles, the source is available here.