i looked into this a while ago myself and did the research on what would also be the best supplements to take.
i ended up going with RegenR8 from the BodyScience range as it had good levels of the 3 key ingredients needed and also Manganese which apparently aids in absorption of the ingredients below...(and the price was inline with most other supplements out there)
Glucosamine HCL750mg
Chondroitin Sulfate (Shark)300mg
MSM (Methylsulfonyl Methane)200mg
www.bodyscience.com.au/page/supplements/flypage/product_id/113Body Science seem to also supply lots of football teams and all kinds of other sporting professionals which i thought must mean they make a quality product - check the website here.
www.bodyscience.com.au/page/bodyscience/teamApparently it's important to take both the Glucosamine HCL and Chondroitin Sulfate together...taking just one on their own is less effective (or ineffective....not sure it was a while ago that i looked into all this stuff)
The bees knees

one that was recommended to me use was CosaminDS - but it is a product from the US and came with the price tag to match and so i just ended up going with the BodyScience product as the ingredients/levels were much the same.
More info on it here
www.biocel.com.au/data-sheet.htmlwww.vitasentials.com/cosamin_ds.htmAlso like mentioned above - Fish Oil was another recommended ingredient to take and i might try the Gelatin out too.
And doing forum searches on things like "knees" or "Glucosamine" will hit you will heaps of talk on this topic.
and finally plenty of reading on it all here
www.kneeguru.co.uk/knees....i hate em, i want a new set please