Exo 28:28-31a; Numbers 18:21-32; Leviticus 27:30-31; Deut 14:22-29; Neh 13:10-12. God's simple system of giving back to Him from what is already His was the Tithe; the first 10% from the increase of our labors - produce and flocks and herds. It was to be used to support the worship, provide for the Levites (who "tithed from the tithe" to support the priests) and every third year provide for the poor and needy. The wisdom literature of the Bible has much to say about the accumulation of wealth and our attitude towards it. The Tithe was abused by Israel - either neglected (Mal 3:10) or taken as a substitute for a righteous life (Amos 4:4) - the prophets frequently confronting the people. Later a minutiae of burdensome laws were attached to it leading to further abuse in NT times. A Temple Tax was later created to make up for the lacking. Nevertheless the Tithe is the only figure God has given as acceptable. Also significant regarding giving in the OT are the special offerings taken for the Tabernacle (Exo 25) and the Temple - David's prayer in 1 Chronicles 29 is a key passage on giving - emphasizing it all belongs to God already. There are only four references to the Tithe in the NT.
In the teaching of Jesus there was a radical call to a self-denying discipleship that lays up treasures in heaven, not on earth. Jesus' parables frequently refer to the stewardship of money, wages, etc. Jesus made strong statements regarding the perils of "mammon" - such as his suggestion to the rich young ruler that he sell it all. He and his disciples lived simply from a common purse and the generosity of others, and he emphasized a concern for the poor and for sacrificial giving (the widows alm). In the early church in Jerusalem, there was a voluntary holding of goods in common. From this model of giving developed the ideals of monastic poverty often taken to extremes in Christian history.
Every one of Paul's epistles mention money, and there are numerous passages on giving: Romans 12:8, 13; Philippians 4:10-19; and most significantly 2 Corinthians 8 and 9 where he writes concerning an offering for the saints in Jerusalem. He emphasized giving as a response to God's gift of salvation (8:9; (;13-15). There is no mention of a percentage - rather it is to be given freely and generously (9:5-8) from a willing heart. Paul taught that giving was to be done regularly (1 Cor 16:1-3); according to or beyond our means and ability (8:3, 12); that none might be lacking (8:13f); not grudgingly or under compulsion, but cheerfully (9:7) as a measure of our faith. He emphasizes what God gives and also suggests that God will respond with blessing (9:8-11). There is also a strong emphasis on accountability in collection and administering gifts. Paul stresses a productive work ethic, working hard, that we might have more to give. So why doesn't Paul mention the Tithe? It seems that he is concerned for a giving spirit that responds to God's Gift in Christ accordingly - the tithe is just a "minimum" - the Christian ought to be giving far more, especially for the work of God in advancing the Gospel.
The best article I have found on giving is Funding and the Kingdom of God: A Biblical Blueprint by Henry Krabbendam (pdf)
An excellent book on what the Bible teaches about wealth and possessions is Neither Poverty nor Riches: A Biblical theology of possessions by Craig L. Blomberg. (a review)
See also On the Pilgrim's way: Christian Stewardship and the Tithe by John K. Brackett
Matthew 10:9-15; Luke 10:3-9; 1 Corinthians 9:1-15; 1 Thessalonians 5:12-13; 2 Thessalonians 3:9; 1 Timothy 5:17-18 There is very clear teaching that laboring in the Gospel ministry is "worthy of its wages." Even when Paul chose to seek his support otherwise, he acknowledged such would have been his "right" as an apostle.
Philippians 1:5; 4:10-19; 1 Corinthians 16:6; 2 Corinthians 11:8-9; Romans 15:23-25; 16:1-2; 3 John 6-8. Paul seems to have been usually supported by his sending church (Antioch) and previous ministries (especially the Philippian's church as he progressed on his missionary journeys. He deliberately chose not to take support from those ministered to as a way to not compromise his Gospel ministry. There were many traveling teachers about that were very much interested in gain, especially patronage from wealthy women. So it appears that when support is taken it should not compromise the integrity of the Gospel. In church history we find many examples of State Supported or denominational supported Ministries - and a history of struggles to keep the Gospel ministry out of political controls. Sending ("raised" supporters) are encouraged by the Scriptures (See especially 3 John 6-8)
Acts 18:3,5; 20:33-35; 1 Thessalonians 2:1-12 especially vs 9; 2 Thessalonians 3:7-13; 1 Corinthians 4:8-14 especially vs 12; 1 Corinthians 9:15. Paul sometimes chose to work with his own hands when necessary in his ministry. Rabbi's were expected to have a trade. At times, Paul did it deliberately in order to set an example for others. However, working all day with leather and teaching late into the evenings at Corinthian was wearing - when support from outside arrived via Timothy, Paul was quick to put aside his "tents" and devote himself full time to his ministry.
Along with a plan for reducing Debt, Saving and living within your means, Tithing by its very nature makes for good financial practice and planning; requiring budgeting and watching spending carefully. Ideally: a 10% Tithe should be set aside first; then 10%- 20% for savings (for the future, emergencies), then the remaining 70%-80% for "essentials - living and housing expenses, food, clothing, including taxes, children's education, etc." and "non-essentials."
Two good Christian Writers on how to deal with debt, budget, save, and give are (the late) Larry Burkett and Ron Blue who have many books on the subject: Wealth to Last by Larry Burkett and Ron Blue ; The Family Financial Workbook: A Practical Guide to Budgeting and Debt Free Living by Larry Burkett; Master Your Money and Generous Living by Ron Blue are among many other useful titles.
The more money one makes, the higher percentage one ought to give away. With time, as our "non-essential" income increases then we deliberately continue to live at the same level and proportionally increase our "tithing percentage" on the increasing income rather than increasing spending on our lifestyle, accumulating goods, etc. So we give for example 15% on the first $5,000 over; 20% on the next, etc. It also involves an application of the Christian "work ethic" (industry, frugality, charity) to a believer's life. The concept was suggested by Ron Sider in his Rich Christian's in an Age of Hunger, despite some of the flaws in that book, the concept is a good one.
Giving God an opportunity to give through us, by looking to Him to provide beyond our known sources of income (2 Corinthians 8:3 "For they gave according to their means, … and beyond their means, of their own free will") either through increased or unusual sources of income; by decreasing our expenses, or moving us to sacrifice. It is a faith exercise - a promise prayerfully made with God, that as He provides you will give, then trusting God to provide; and unlike a church pledge, a matter only between the Lord and the giver.
For more on Faith Promise Giving see Faith Promise Page, his Faith Promise FAQ and J. Oswald Smith's Faith Promise Bulletin Insert. Faith Promise Giving programs are used by many denominations and churches including Presbyterians, Christian Reformed, Methodists, Nazarenes, etc as well as many missions and other Christian Works. Many can testify as to how God has provided in unexpected ways.