My favorite defunct logo in all of hockey is—by far—the Oakland Seals design. And I'm doubtful that I'd have ANY company with that opinion. No matter what hockey logo site or hockey blog I visit, everyone seems to give the Seals logo a good beating.
There are a few version of the logo, which pretty much depends on the name they wanted to go with on any given week. They were first named California Seals; renamed the Oakland Seals part-way through the 1967–68 season, and then to California Golden Seals in 1970.
In today's NHL, all those logo design changes would mean a shit-load of jersey and merchandise sales!
I love the above logo because of the bold colors, bold lines, and clever use of the "O" for Oakland.
The color scheme of royal blue, kelly green and gold works much better for me than the logo's color scheme of just green and gold, as pictured here. The royal blue and black really makes the logo pop. And I think the above version makes better use of white/negative space. The green/gold version looks a little sloppy, has weak line weight, and the stick is out of proportion.
As for the word-mark ... well, it is utter crap. See for yourself.
I enjoy the creative sports designs of the 70s, but they can be hit or miss. This word-mark is a definite miss. Awful colors, awful type choice and that thin "e" just really makes this a bad word-mark in my opinion.
Here are a couple pictures of their jerseys, along with the Cleveland Baron's gem of a jersey (which the Seals would later become after bolting California).
SealsHockey.com has a great archive of photographs to browse, but watch out — there's some baby blue uniform images sprinkled within the pages of all that green and yellow! Baby blue will just never work.
For you media guide nerds, here are all the media guide covers for the Oakland Seals.
Oakland Seals Wikipedia.com page HERE.