I use Feelgood30 over 15 supplement - has all vits/mins plus joint supplement - my lad is going great on it - best Ive tried, someone else on my yard swears by Feelgood30 Joint supplement, but Ive never tried it mysel.
Both my arthritic heavies are on Feedmark's Extraflex HA. Have noticed a real difference in them, plus Feedmark are always doing offers (Buy one get one free at the mo I think)
I use coequin as it has scientific proof that it works and it really has for so many horses at my yard!!! I get it from america though and it costs about 100 with p&P for 1500g which is enough for a 500k horse for about 9 months so very good!!!! PM if you want his e-mail address
I use NAF Superflex but it does cost a fortune, every time I have taken my girl off it she has seemed a little unlevel (it my just be me imagining it though!) and I end up just buying it for piece of mind. Such a sucker for the 5* vet approved advertising :s