LVM is at least as powerful as NSS pools, you can extend volumes to free space on existing disk, or add new disk and extend the volume group to include the new disk. You can also do volume level snapshots.
Reiser and XFS partitions can be extended on the fly to grow to the size of the bigger volume. Ext3 will require unmounting, extending and remounting.
EVMS is even more powerful, but I'm not as familiar with that as I am with LVM.