Although there are many Vrat (fast) of many types which have been prescribed here and there in Puraan etc religious scriptures, but here are some Vrat and Fasts which are not listed at one place and are scattered here and there individually, as a suggestion from great Muni and Rishi to people for some purpose.

(1) Solar and Lunar Eclipses - Vishnu says - "Donations during solar eclipse give fruits 10 Lakh times. If solar eclipse is on Sunday, or lunar eclipse is on Monday, it is called Choodaamani Yog. Bathing and donating during that time give eternal fruits."
(Padm Puraan, p 180)

(2) Shraaddh - Vishnu says - "There is no greater Yagya than doing Shraaddh. Whatever is given as donation in this, that is all immortal. Whatever is given to others, its fruit is 10,000 times. Whatever is given to one's own caste people, its fruit is one Lakh times. Whatever is spent in Pind Daan, its fruit is 10 million times; and if it is given to a Braahman its fruit is multi million times.
(Padm Puraan, p 180)

(3) Shraaddh on Eclipses Days - Vishnu says - "Who does Shraaddh on Amaavasyaa, Yug beginning days and solar and lunar eclipses days, he goes to eternal Lok.
(Padm Puraan, p 180)

(4) January Sankraanti (Makar Sankraanti) - Daan on this day is eternal.

(1) Vaishaakh Shukla 3rd (Akshaya Teej) - Daan is eternal on this day. In fact the whole Vaishaakh is a sacred month. One should keep fast, especially during the last five days, and donate something - sesame seeds, water, gold, cereal (Ann), sugar, cloth, shoes, umbrella, lotus flower, conch shell, pitcher etc. Snaan, Dhyaan, Vrat, Fasts done in this month are all eternal. Taking bath on even three days in this month - Trayodashee, Chaturdashee and Poornimaa, destroys all sins. Who feeds a Braahman and donates black or white sesame seeds after taking bath on these three days, his all sins of life time are destroyed.

(2) Jyeshth Poornimaa - Vashishth Jee advised Diti this Vrat for mental peace and happy married life after she had lost her many sons and grandsons in Devtaa-Daanav war. She had Marut Gan as her sons after this Vrat. 
(Padm Puraan, p 19)

(3) Bhaadrapad Shukla 7th and Sankraanti on Sunday - Take a flower and meditate on Soorya Dev, then smell the flower and throw it towards Eeshaan (North-east) direction. Later worship him with sandalwood paste, Dhoop, lamp, sweets and water. All Daan, Tap Jap done on this day are eternal.

(4) Maagh Shukla 3rd - Daan on this Tithi is also eternal.