The Bolter and Chainsword is the premier site for all your Power Armour needs.
Dealing soley with the Adeptus Astartes it is an excellent source of modeling ideas, tactics and general forty kay chat.
Also home to the now legendary B&C Space Marine Painter, an outstanding tool for designing your own DIY colour schemes.
I've been a member for around five years now and I highly recommend the site.
Be warned though, it is strictly space marines only.

LINK: Bolter and Chainsword