I'm not Doc, but for the more common (and most uncommon) ICs both digikey
are decent sources. Sure they'll be more expensive than you might be able to find on e-bay and electronics wholesalers(with some the term is used loosely); but they have an dependably acceptable level of quality for the products they sell (versus the hit-or-miss you often get by extreme bargin hunting), actual customer service (including basic stuff like datasheets and other documentation), and significantly faster delivery if you are in North America. I also like to patronize the smaller online electronics vendors (like some of those listed on the Arduino Distributors
list, but they of course have a more limited selection.