Lately, I've found it very hard to shop for wood at the local big box stores. The quality of pine will vary wildly, and I don't have time to sort through 10-12 foot planks looking for the ones that will yield the most boards.
I strongly recommend using the good folks at BreakingBoards.Com Their web site isn't pretty, but they're selling boxes of wood, for Pete's sake!
I have used their wood for a few testings now, and I have found it worth the extra price. Every piece of wood is excellent and free of knots, warping, staples, sap, etc. They are sent in easy to transport cubic boxes (with a pleasing pine aroma added at no charge) and they ship quickly. Shipping is expensive, but it's a 25 pound box, so you have to expect a little premium.
Compare this to:
1. Going to the big box store.
2. Sifting through the wood.
3. Picking wood and waiting for someone to cut it (or transporting the planks and DIY)
4. Sorting the wood into various grades (OK, Bad, Horrible)
5. Burning 30% of the unusable wood in your fireplace.
All in all, I would highly recommend their services, and no, I'm not getting any free boxes for this review. :)