I order lumber all the time. The two I use most frequently are Niagara Lumber: https://www.niagaralumber.com/index.php?cID=1
and Green Valley Wood Products: http://www.gvwp.net/category/56-lumber.aspx
Niagara has a better selection and thicker stock available; Green Valley has better prices. I've purchased about 100bf of 4/4 cherry from Green Valley over the past few months. Their quality is top-notch and they usually ship the same day I order.