The six Shaiva-Purānas are Matsya-, Linga-, Skanda-, Kūrma-, Shiva-, and Agni-Purāna. The Agni-Purāna is sometimes replaced by the Vayu-Purāna, apparently the oldest Purāna.
Source: The Encyclopedia of Eastern Philosophy and Religion: Buddhism, Hinduism, Taoism, Zen. Shambhala Publications, Inc.
Documents on the Shaiva-Purānas
Books on the Shaiva-Purānas
External links: Puranas / Mahapuranas
Shiva-Purana / Agni-Purana / Linga-Purana / Skanda-Purana / Kurma-Purana / Matsya-Purana