Not being close to any LHBS I've grown to rely on MoreBeer for nearly all of my supplies. When buying 50-70 lbs of base grains, it's difficult to beat their 10 lb. packages at just over a $1.00/lb. including the shipping. The 10 pounders are much easier to handle, store, and keep fresh, too.
Some of their specialty grains are slightly more expensive, and I'll sometimes get those from other sources such as Brewmasters. I'll agree that getting the orders "picked" and out the door is a bit slow sometimes, but it seems to me that it's been better of late. They are good about warning you when a shipment may be delayed for one reason or another.