Unfortunately the good supplements are a bit pricey but worth it. Dasequin is one of the best. I use Purica Whole Body Health and Joint powder. I find it is reasonably priced and if you get the extra strength you can cut to half dose for maintenance after a few weeks.
Cosequin is the next best thing. Dasaquin and Cosequin are made by the same company and very similar. But Dasaquin is the best for severe joint issues.
I like Springtime Inc's Joint Health and Fresh Factors. But also consider adding fish oil. One of the surgeons we saw highly recommended fish oil to help with our girl's arthritis.