Some time ago the Ubuntu kernel team started generating installable mainline kernel builds. These are kernels built directly from Linus' tree with no Ubuntu modifications. These are generated from each tagged release which includes all full kernel releases (2.6.x, 2.6.x.y) as well as the release candidates (2.6.x-rcN). These kernels have proven very popular both with people wanting support for the latest hardware and as a basis for finding the source of bugs.
As an experiment we are expanding the scope of the mainline builds to include builds of the daily snapshots of the tip of Linus' tree. These are generated every 24 hours where updates are present and are published in the mainline builds archive as normal.
For more information on what mainline builds are, why you might want them, and how to obtain and install them can be found on the Ubuntu WIKI on the mainline kernel builds page. Enjoy.