Some major Hindu Festivals:

festival	time	(major deity)	significance / practice
Divali	Oct / Nov	Rama / Krishna	Light symbolism; triumph of the gods in curbing evil
Makar Sankranti	Jan		end of harvest; celebrating the beginning of the sun's northward movement, beginning of the more auspicious half of the year
Shivarati	Feb / Mar	Shiva	marriage of Shiva to the goddess Parvati
Holi	Mar	Krishna / Holika	throwing color, re-enacting Krishna's youthful pranks
Ramnavmi	April	Rama	Birth of Rama
Ratha Yatra	Jun / Jul	Krishna	Krishna as Lord Jagannath (Juggernaut)
Raksha Bandhan	Aug	(Indra)	sister ties protective thread around brother's wrist
Krishna Janamashtami	Aug / Sept	Krishna	Birth of Krishna
Onam	Aug / Sept		Harvest festival in Kerala
Ganesh Chaturthi	Sept	Ganesha
Navaratri / Durga Puja	Sept / Oct	Godess / Durga	nine nights of dancing in honor of goddess Durga who is the destroyer of a demon
Dashera	Sept / Oct	Rama	tenth night, Rama's victory over Ravana