I came across this a couple of days ago, but the links did not work
until recently. It may be useful to some of you if you are thinking
about a new purchase or have equipment that you wonder whether it
should work. Canonical has published a list of equipment known to work
with Ubuntu.

There are two links:

The first is for components by manufacturer:
http://www.ubuntu.com/certification/catalog
The second is for machines by manufacturer: http://www.ubuntu.com/certification

It is supposedly the largest such database for any distribution.