Kupala/Kupalo - the deity of summer and plants (especially herbs). Some Slavic tribes view Kupala as a goddess, sister of Morana, and some - as a god (under the name of Kupalo), brother and husband of Morana. Anyways, according to the myth, every spring the god Jarilo/Yarilo comes to the human world to bring new life and abundant crops. He grows older as the day grows longer and on the day of the summer solstice (June 22nd), when the day is the longest, he turns into Kupalo - the god of summer. So, Kupalo is the adult Jarilo. The eve of June 22 is called Kupalo's eve. It is believed that that's a magic time - the trees have the power to speak and move and herbs and other medical plants collected that night have super healing powers. Kupalo stays around until around late September when he goes back to the svarga (the gods' world) and Marena takes over.
Lel - a minor god of love, son of Lada and twin brother of Lela. According to the myth, he is a young man dressed in white, with a flower wreath on his head. He is a companion of his mother Lada and the patron-god of marriage and family.
Morana/Morena - originally the goddess of winter and by default - the goddess of hunger, cold and death. Her name is derived from the Slavic "mor" - death. She is the sister of Kupalo, but, whereas he brings life, she brings death. She lives in the underworld with the souls of the dead (a.k.a. "mori") and ascends to the human world in the winter. According to the Slavs, that's why winters are cold, the grain and meat are scarce and death prevails. In the "divine hierarchy" she is under the ultimate master of darkness, Chernobog, but nevertheless, she possesses some wicked powers herself (buahahahaha!).
Ruevit - the god of the light and heat, protector of fertility and crops. To the Western Slavs he is known as Rugievit, as they believe he lives on Rugen (an island in the Blatic sea). Ruevit has seven heads, seven swords in his belt and one sword in his hands. Each of the seven heads and seven swords watch over and respectively protect the crops in each of the seven fertile months of the year. The Southern Slavs who used to grow vines and make wine, also consider him the parton god of wine-making.