I buy a lot of my wood at a local place that sells wood to restaurants. Their chunks are nice solid fist sized pieces that come in a large "onion" bag, and they last me a long time.http://www.woodyardbbq.com/wood_merged.html
I can also pick up a nice sized bag of chunks at Ace Hardware...they have a surprising variety of woods and a decent seasonal display of grills, smokers, and other goodies.
I have recently been scanning craigs list for larger quantities, as I want to build a stick burner for competitions. I stumbled into a truck load of apple wood for free...I just had to go pick it up! If you don't look on craigs list, you should.http://www.smokingmeatforums.com/for...ad.php?t=75226
There are a lot of places on the web that sell different varieties of smoking woods...just google smoking chunks and see what pops up.
Ebay has a lot of people that sell wood as well. In a pinch you could entertain buying something from there.