First of all, then, I urge that supplications, prayers, intercessions, and thanksgivings should be made for everyone, for kings and all who are in high positions, so that we may lead a quiet and peaceable life in all godliness and dignity. This is right and is acceptable in the sight of God our Saviour, who desires everyone to be saved and to come to the knowledge of the truth. For there is one God; there is also one mediator between God and humankind, Christ Jesus, himself human, who gave himself as a ransom for all.

Revelation 5:8

When [the Lamb] had taken the scroll, the four living creatures and the twenty-four elders fell before the Lamb, each holding a harp and golden bowls full of incense, which are the prayers of the holy ones.

Revelation 8:3-4

Another angel with a golden censer came and stood at the altar; he was given a great quantity of incense to offer with the prayers of all the holy ones on the golden altar that is before the throne. And the smoke of the incense, with the prayers of the holy ones, rose before God from the hand of the angel.

Other passages worth checking out:

Colossians 4:3 & 1 Thessalonians 5:25 - "pray for us"
2 Thessalonians 1:11 - "we always pray for you"
2 Thessalonians 3:1 - "finally brothers, pray for us"
Ephesians 6:18-19 - "Pray in the Spirit at all times in every prayer and supplication. To that end keep alert and always persevere in supplication for all the saints. Pray also for me, so that when I speak, a message may be given to me to make known with boldness the mystery of the gospel"
Tobit 12:12 - the angel presents Tobit and Sarah's prayer to God

Also check out the Catechism of the Catholic Church on the Topic

CCC 618 - Apart from the cross there is no other ladder by which we may get to heaven.
CCC 970 - Mary's mediation
CCC 1349 - We even intercede for others at Mass in the General Intercessions
CCC 2636 - The intercession of Christians recognizes no boundaries

Finally, check out what St. Thomas Aquinas said about the topic (Summa Theologiae III, 26, 1)

A mediator brings together those who are separated: for extremes are united at a midpoint. Now to unite men to God perfectively belongs to Christ, through Whom men are reconciled to God. And, consequently, Christ alone is the perfect Mediator of God and men, inasmuch as, by His death, He reconciled the human race to God. Hence the Apostle Paul, after saying, "Mediator of God and man, the man Christ Jesus," added, "Who gave Himself a redemption for all." However, nothing hinders others from being called mediators inasmuch as they cooperate in uniting men with God by directing their way or by ministerial actions.