I visited here today, and met the horses that Mr Brand mention below. They behaved themselves with me though - I asked them to stand in the top corner of the field so that they wouldn't be in any of my photos, and they duly obliged. A lovely pair of horses!
But back to the stone. It stands on a very slight mound, and what appears to be a few packing stones can be seen at it's base poking through the grass. Fred Coles described this in 1910 as the last remaining stone of a stone circle, although he didn't offer any reasons as to why he thought there were more stones originally.
This stone is situated in a field to the south of the A85 Crieff to Lochearnhead road, near the village of Comrie. There is a small track down the side of the field and you can park here as long as you don't block the road. The stone itself is around 6-1/2 feet tall, with no discernible markings on it. There were a couple of friendly horses in the field when I visited today, which made photographing the stone rather interesting!
Directions - head W from Perth on the A85 through Crieff towards Comrie. Approximately 4 miles after Crieff, not long after the signs for the Braincroft Bunkhouse, you will see a long thin field on your left, flanked on either side by an avenue of large trees. The standing stone is clearly visible 100m into the field, on the left hand side, close to a small wooden stable. Carry on past the field, and you will come to a layby you can park in, and walk back to the field. The easiest way in, without disturbing the horses, is to head to the left edge of the field boundary wall, and climb over the wooden fence. There is a fence within a fence here, so walk down through the trees until you are level with the stone, then hop over the inner fence to get to the stone.