The LadderLimb is an third-hand accessory that fits inside ladder rungs, such as those found at the sides of aluminum ladders.
It features a tapered shaft, a handle to help with positioning, and a swiveling carabiner clip that can support tools, paint pails, buckets, tool bags, or anything else you might need while on the ladder.
The LadderLimb is priced at $30 each, and discount pricing is available for packs of 6 and 12.
There doesn’t seem to be a weight rating for the LadderLimb, but you probably won’t want to suspend more than a few pounds from it anyways. A 5-gallon bucket, for example, would not be a good idea to hang.
More Info(via LadderLimb)
Update: the LadderLimb can support up to 22 pounds of weight.