I am a happy and heavy user of two HP Microserver Gen8 machines. I must quote the best online resources for the Microserver enthusiasts:
The amazing German forum thread at www.hardwareluxx.de
The long and extensive English forum thread from homeservershow.com
The official parts page from HP
Always is good to hunt for bargains at Amazon.co.uk. You could snatch a 85% discount for a lots of HP Microserver stuff.