Last year at the Hearth and Patio Show in Atlanta we met the good folks from MaineCookingWoods.com and they gave us some samples. I just finished my last batch and have reordered from their really easy website.
I consider this company to be a good source for your wood and today I ordered more sugar maple chunks and black cherry chunks. I like the chunks better than the chips, but I consider this just a personal preference.
When I am firing up my Weber, I use two or three pieces. For best results, soak the chunks overnight in water and just add them onto the coals when the coals turn ashy grey. Experiment with the different types of wood and discover how the subtle smoke flavor can accent your food.
WARNING: Remember smoke should be an accent flavor and not a predominant one. Too little is better than too much!