http://miniaturemarket.com/
Miniature Market has some of the best prices on cases, bulk discounts on multiple cases (buying two cases will get you a full set or close to it), and lower than Ebay prices on singles. Shipping on any order over $75 is free and they ship fast. You will have your package in 2-3 days, unlike some places who will take your $12 for priority mail, wait 10 days to even ship them out, then send them via UPS. I won't name names, but.. Paizo. It's Paizo. Paizo also charges 2-3 times market price for singles and the singles "may or may not" be bagged or carded. Who knows? Paizo is pretty much your worst choice for miniatures.
Another good place to get singles is
Noble Knight Games. Their prices are comparable with Miniature Market, sometimes a little more, sometimes a little less. However, the important thing is that figures from the older sets are getting pretty hard to find and what you can't find at Miniature Market, you may find at Noble Knight. Noble Knight also ships quickly, but they don't offer free shipping.
The cheapest place to get cases in my experience has been
Game Outfitter. They beat Miniature Market by a few dollars, but they do not sell singles. I can't recall how quickly they shipped, because most of my orders have been with Miniature Market.. I like to pick up other things while I'm getting my cases.