I take glucosamine chondroitin and it works for me, a while back I went about a month without taking it and my knees would hurt and "pop" every time I extended my leg out. Although most glucosamine is from shellfish you can find sources from plants. I consider myself vegan but I do take the glucosamine that is derived from the shellfish. I bought about a years supply 6 months ago before I knew that plant sources existed, when my animal-derived supply runs out I'm gonna buy the plant derived source and see how that compares.
I can honestly say that I think Glucosamine Chondroitin is great for people with knee problems. I'd be crawling around on the ground (or driving) if it didn't exist!