Number Sets: Gelug

Two
Two Protectors, Red & Black (Nechung & Lhamo)

Three
The Three, Guhyasamaja, Chakrasamvara & Vajrabhairava.
The Three Ku, Ngog & Drom (Kuton, Ngogton & Dromton).
Three Great Monasteries: Ganden, Sera, Drepung.
Three, Father & Sons (Tsongkapa, Kedrub, Gyaltsab).
Three Lord Manjushri (Sakya Pandita, Longchenpa, Tsongkapa).
Three Omniscient Brothers (Atisha, Dromton and Putowa).
Three Protectors, Shadbhuja, Yama Dharmaraja & Vaishravana.
Three Wrathful Ones Combined (Vajrapani, Hayagriva, Garuda).

four
Four Deities of the Kadampa (Akshobhya, Avalokiteshvara, Tara, Achala)
Four Schools of Tibetan Buddhism (Nyingma, Sakya, Kagyu, Gelugpa)

Five
Five Forms of Tsongkapa

Eight
Eight Panchen Lamas
Eight Wrathful Ones of the Gelugpa School

Fourteen
Fourteen Dalai Lamas

Seventy-five
Seventy-five Lords of Pure Lineage (Shadbhuja Mahakala Retinue)

Jeff Watt 4-2006

(The images below are only a selection of examples from the links above).