I second the BBB post. They have the largest selection outside of an online store. I have gotten some at HomeGoods before for a very good price. Not a lot to choose from but super cheap!
Was just at Bed Bath and Beyond today and their selection is great. They have tons of new Starbucks flavors and had some great seasonal ones like pumpkin spice, white chocolate mint, and mudslide.
I also suggest bed bath and beyond. We got the hot apple cider, hot cocoa, two types of coffee and a decaf tea on sale a few weeks ago. It also helped that we had a coupon.
While they don't have a lot of variety, Costco usually has a great price.
I have also used bigcatcoffees.com to buy variety packs. It is nice to buy just a few of different flavors. If you don't like them then it is not a waste.