When we talk about weapons of Vishnu, it would do justice only if we begin the series with Sudarshan Chakra. From Mahabharata to Gajendra moksha, it's Sudarshan Chakra that's widely praised about.
@Itishree001

It is said that Sudarshana Chakra will work on the command of Vishnu and doesn't wait for his orders but could pick up directly from his thoughts and hence is the most swift weapon.
The Sudarshan Chakra is worshipped in temples in dedicated mandir across India.

Sudarshan Chakra Powerful weapons of Maha Vishnu Sudarshana Chakra Circular disc with serrated edges with ability to spin and attack the enemies at the command of Vishnu.

Sphurad sahasrara Shikhandi theevram, Sudarshanam Bhaskara koti thulyam, Suradvisham prana vinyasa vishnu, Chakram Sadaham saranam prapadye

I surrender always to the Vishnu's wheel, Which is sharper than thousands of flames, Which is equal to billion suns, And which takes out the life of Rakshasas.

Vishnor mkhothonila poorithasya,
Yasya dwanir Dhanava dharpa hantha,
Tham Pancha janyam, sasi koto shubhram,
SAnkham sadaham saranam Prapadhye.

I surrender always to Lord Vishnu’s conch,
Which makes sound due to the air from mouth of the Lord,
Whose sound humbles the pride of Rakshasas,
And which shines like billions of moons.

Credit... @findingtemples