The Seagate Momentus Hard Disk has been one of the best notebook drives to come out, with the exception of the Hitachi 7200RPM models that is. It's one of, if not the fastest 5400RPM notebook drive out there.
Its construction matches that of all other 2.5" drives; it's light weight so you're not lugging an extra brick inside your notebook. It runs extremely cool, so not to add to heat which is especially important in the HTPC and notebook market where most of these run with only one fan. Furthermore, its capacities continue to grow; the 250GB model is large, but there are 320GB and 500GB models in the fourth generation already making their way to market.
With a good price tag, high performance and a long warranty period, the Momentus 5400.4 is a definite drive to have for the HTPC and notebook environments.