There's Porches, on the way between Horsted Keynes and Chelwood Gate, 01825 740644.
I don't know what they are like, I just know of them through someone else.
There's the buckley's place which is hook farm, in between west hoathly and ardingly. AMAZING grazing, nice school with lights and jumps, internal boxes and good hacking on trot roots. Other than that there's a great yard in sharpthorne owned by Adrian but I can't remember what it's called but hopefully someone else can. I looked round and it was really good, more of a competition yard with really good facilities for a DIY yard. Only reason we didn't go there was because we needed part livery and it was out of my budget.