MCM Electronics:
http://www.mcmelectronics.com/Default.aspx
They're an "associate" of Newark/Element 14 and they sell Pis at the official prices.
Ameridroid:
http://ameridroid.com/t/raspberry actually sells the Pi3B for $0.05 under the official price ($34.95 instead of $35.00). Everyone else I know of marks the price up. If you live near them, Central Computer sells the Pi3B for $38, which means that for a single board, it's cheaper than paying shipping from a company in the official supply chain (e.g. MCM, Allied, or Newark).
Now if Ameridroid could just get hooked into the Pi Zero supply chain we'd have two mail-order sources in the US.