Our 8 yr old lurcher gets a tablespoon (1500mg) of glucosamine liquid with his breakfast every morning. Its human grade from the supermarket and has really helped him. He was starting to get noticeably stiff after getting up from the floor and now seems to have no problems after a month or so on it. Also a lot cheaper than the same stuff from the vet!
I recently started my Springer on Yumove tablets, which contain Glucosamine, Chondriotin and Omega 3. Have noticed a difference already. Cheap from animeddirect.com and they do free postage
Feedmark do various supplements. We got our oldie a magnetic collar a few years back (we were partly sceptical but thought it couldn't hurt to try). He improved so much and didn't get half as stiff. He is 15 now and still doing pretty well
She was on Equimins Flexijoint, Cod Liver Oil, Previcox and Tramadol but was still so unhappy we were close to having her pts. Since introducing the turmeric she is completely off the Previcox and Tramadol and is like a puppy again (albeit a 13 year old one)
I've no idea whether the Flexijoint or Cod Liver Oil are doing any good (I suspect the turmeric would probably be sufficient on its own) but I'm just happy to have her off the arthritis drugs and for her to be so happy.