I've ordered all mine online. Malaysian driftwood has a lovely dark colour, and I've found good deals on sites like eBay or Amazon.
Alternatively, if you have a large tank and want something branchier, I ordered large amount of Manzanita from Manzanita Burlworks for a very fair price. I believe you have to order by phone, but the guy that runs the place is fantastic - I told him the measurements of my 55g, the tank opening measurements, and the look I was trying to achieve (mangrove roots spreading down into the substrate) and he made sure to send me plenty of pieces that fit perfectly in the tank and achieved the look I wanted. I got enough for the 55g plus some extra for I believe around $45 or so.