Not for laptops anymore, as far as I know. They still sell their Inspiron netbooks with ubuntu, though (8.04).

I see 4 laptops and 1 netbook at http://www.dell.com/us/business/p/laptops#facets=80770~0~179... (use OS filter if link doesn't apply) different models running 9.10, 10.04, 10.10. For some reason the link on dell.com/ubuntu only shows the two Latitudes, not the three Inspirons.

Not major manufacturers, but also see Zareason and System76.