I have found Tony's Train Exchange an excellent resource for DCC Supplies as well as some Peco Code 75 track. Quick communication and postage as well as very competative pricing. Here in Portland, I frequent the Hobby Smith mainly for Digitrax decoders and scenery supplies. The Whistle Stop is also very well stocked but a ways away over in East Portland. For British outline, I have used Britannia Models just over the border in South Surrey, BC Canada.
For other overseas orders, I have also used Hattons who don't charge VAT which offsets the postage!