From central Mexico, Mammillaria apozolensis var saltensis is an aptly named clumping thin stemmed cacti sometimes called "Lady Fingers". The stems are thin and elongated and offset furiously, soon producing small clumps. It's an excellent choice for a hanging pot. Spines range from gold to red and are mostly harmless as most varieties lack centrals.
The one above is a variety called "Copper King". It's been forming a nice clump in my garden. Below is a pink flowered form. The flowers are usualy yellow.