I wear a Salamander Golden Retriever (specs can be found here
I mostly bought it because it did double duty as a flip line for when I'm rafting (the tow line works well as a flip strap).
Not cheap, but its well made with Cordura, and quality rope. I've never used the tow line to tow a boat, (actually I've never towed any Kayak anyway), but I assume it would work just fine as it has a quick release.
EDIT TO INCLUDE:
I have friends that prefer the NRS versions
. It is nice that the NRS ones can "pop out" of the belt in order to be thrown. YMMV.
They don't have the tow attachment.