I would also recommend the King's Arms in Westerham but it was absolutely dead when I stayed there. The room had the squeakiest floorboards I've ever known, so much so that I felt guilty about walking on them, out of concern for the poor person in the room below. There's not much else happening in Westerham.
The Croydon Park is reasonable but lacks character. If you do stay, try the dinner buffet - if you fully partake of the starter you'll find it difficult to find room for the main course.
I've also used the Jury's Inn in Croydon town centre - OK if you don't mind a highly average breakfast on a tray.