Sarah Lurie (IronCore Series) is good if you don't want to invest a ton of money. Her dvd's are very reasonable. Lauren Brooks is good....but pricey. Andrea DuCane as mentioned. ArtofStrength has a lot of workout dvd's and downloads.
This looks very interesting as far as instruction goes......
I think I researched her in the past and she does workshops with Mike Mahler so she should be good.
AverageToElite has some great kettlebell correction videos on youtube and I think offers dvd's at their website. (averagetoelite.com)
Swing Like You Mean It- RKC Style
Currently swinging either a single 55 lb. or two 25 lb'ers.