Short overview (for news sites, etc)
Linux 2.6.19 includes the clustering GFS2 filesystem (http://sources.redhat.com/cluster/); Ecryptfs (http://lwn.net/Articles/156921) the first experimental version of EXT4 (aimed at developers), support for the Atmel AVR32 architecture, sleepable RCU (http://lwn.net/Articles/202847), improvements for NUMA-based systems, a "-o flush" mount option aimed at FAT-based hotpluggable media devices (mp3), physical CPU hotplug and memory hot-add in x86-64, support for compiling x86 kernels with the GCC stack protection, vectored async I/O (http://lwn.net/Articles/202449), Netlabel subsystem (http://lwn.net/Articles/204905), allow to disable compilation of the block layer, IDE Parallel-ATA drivers based in libata (http://lwn.net/Articles/198344), Granular IPSec associations for use in MLS environments, add the Netlabel subsystem (http://lwn.net/Articles/204905), Mobile IPv6 (RFC 3775), some new drivers, improved support for many already existing drivers, and many other things.
Important things (AKA: ''the cool stuff'')