As far as I know Kutter HD, and Surdyke are the two big ones that people on this board use. I haven't ordered anything from Kutter in a while, but last I knew they were giving 20% off and free shipping. Someone correct me if I'm wrong.
Kutter HD is still offering discounts and free shipping after 99 spent, just bought the HD diamond back cables from there. Plus Anthony @ Kutter HD is cool and good to deal with.
Ditto on Kutter. They are usually $1 cheaper than Surdyke, but I always check both. Just got edge cut cow bells. Wish they were a little faster though. . . . .
Kutter and Surdyke. The shipping isn't the quickest, but depending on what you'll save it may be worth the wait. Keep an eye on your own dealership as well. There are a few by me that run periodic 20% off sales as well.