Question : What is the best VoIP system for small muli-office business?

I am building a network for a client who will be getting a VoIP phone system.  They will have 2 locations that would be connected to each other.  I will be helping them choose a system and select a vendor to install it, provide some consulting, and some really basic support.  Does anyone have any recommendations of a good system that is reliable, has the ability to integrate between multiple locations, and has good functional options?  Clients are willing to spend money for a good system, but I want to keep it out of the stratosphere if possible.

Answer : What is the best VoIP system for small muli-office business?

The most well known are probably Cisco (callmanager), Avaya and 3COM.

I dont have any personal experience of them. I use Asterisk myself which is an open source IP PBX which I entirely support myself. There are however commercial versions of it which include support contracts.
http://www.digium.com/en/products/software/abe.php