There are three protectors generally associated with Lama 
Tzongkhapa's tradition

1.Kalarupa (Associated with Yamantaka and Manjushri, the wisdom 
Buddhas)
2.Six-armed Mahakala (a wrathful manifestation of Chenrezi, Buddha of 
Compassion)
3.Vaishravana (Dzambhala)

There are many other protectors such as Hayagriva and Paldhen Lhamo, 
but the three above are the ones Lama Tzongkhapa himself practiced 
regularily and also they are the most common.