I too have filleted more fish than most people will catch in a lifetime and, for the money, check out CRKT's 9" big eddy knife.
I like that design, but I use Forcshners, including their big upturned style butcher knife for albacore, and medium sized, and larger salmon. Their fillet knivies are outstanding with a great combination of flexability an edge holding ability. Excellent stainless steel if your using it primarily with salty fish. The CRKT will start to pit after lots of use around salt water. Kershaws are especially proned to this.
The CRKT knife also has the best handle in my opinion.
Also, find a good butchers steel, and learn how to use and maintain it correctly.
I own a couple of Dickeron sapphire-cut steels. Not cheap, but I get the most out of all my knivies, including in the kitchen.