PC Engines released information about their new design for an Alix successor.  The new model is called the APU.
I currently use about 30 Alix based firewalls at work.  They are great little devices, they can handle about 30Mbit/s with traffic shaping enabled, and are completely passively cooled and  very low power.  Specifically I use this model from Netgate, the Netgate m1n1wall 2D3/2D13 red.