We use Synflex here, which is liquid glucosamine. I think it's the best one we've tried (and we've tried quite a few different products over the years). It was recommended by other dog owners.
I buy it from here: http://www.synflexforpets.co.uk/ - it is a human grade product but there's a human version too now which has an ingredient you're not meant to give pets (though I didn't realise the first time and no ill effects thankfully!).
I used to give Mojo the human G&C tablets but she ended up picking them out, so I switched to Jointaid, which has everything in and more. And I don't think it's my imagination but since switching she has had fewer lame/stiff days than before. She has even stopped needing to wear her magnetic collar.
ooh jointaid, nice to hear that recommended. I have some freebie bags in the dog cupboard....keep meaning to read up on it more as I'm thinking of it as a preventatie supplement (can't do any harm can it?)
I do worry about agility with Basil, i'd hate to find out later i've done some harm.