We've been using Liquid Health for a while now. I was getting various human-grade supplements before in pill-form but that was too much of a bother for the BF to add so this has been an easier option.http://liquidhealthpets.com/k9-level-5000
We also use Pet Kelp http://www.petkelp.com/products.html
(the skin and coat formula) because of the overall benefits of kelp in general. They have a glucosamine/chondroitin formula but since we're already adding Liquid Health, I use the skin and coat to supplement Molly's Omega-3-6 intake since fish oil messes up her anal glands.
I know this isn't joint-related but since I know who will be reading this, I also want to recommend local honey (Marshall Farms is available at a lot of local markets) for any possible environmental allergy issues. I don't think Zoey has any allergies but since SF area is a new environment for Zoey, she may go through an adjustment period up here and be affected by pollen - especially in the next few months which are typically very windy and lots of stuff gets blown around. I always start Molly on local honey around this time of year to prep for spring allergies as she seems to be mildly affected by them.