Here are the main passages, and you're familiar with all of them:
* Leviticus 27
* Malachi 3
* Matthew 23

Secondary passages, also addressing the tithe but not used so often for teaching it, are:
* Genesis 14 (Abraham gives 10% to Melchizedek)
* Genesis 28 (Jacob promises 10% to God)
* Deuteronomy 12 (General passage on tithe)
* Deuteronomy 14 (General passage)
* Numbers 18 (Tithes support Levites)
* Numbers 31 (Spoils of war)
* Luke 18 (Pharisee and tax collector)
* Luke 21 (Rich people and poor widow)

1. Lev 27
Tithes on animals and produce. Nothing is actually said about money.

2. Mal 3
Mentions "tithes and offerings." The offerings are those of Lev 1-7, various animal and other sacrifices, as also Mal 1 refers to. Bring the whole tithe into the storehouse, which is the place grain etc are stored.

3. Matt 23
Once again, the tithes referred to are on spices, the lowest division of the category produce. Jesus commends them for this. We are in the world of Judaism. In the same chapter we read of phylacteries, tassels, synagogues, the temple, and uncleanness laws. How do these various items carry over into Christianity, if they carry over at all? Food for thought...

An agricultural tithe for an agricultural society
The worlds of the OT and the NT were highly agricultural. We don't sacrifice lambs, bulls, and goats today in part for the same reason we don't give 10% on them to the Levites: this was required only of the old dispensation. In the same way, most of Jesus' parables were agricultural.

In sharp contrast, the agricultural sector of our economy is quite small. Goods & services, on the other hand, is quite large. How do you give 10% on goods acquired and services performed for you? Not only is it tricky to categorize these things, they lie outside the pale of agriculture, which is the only area covered by the tithe.

1. Genesis 14.20
Abraham gave Melchizedek 10% on goods and possessions. Verse 11 is probably exactly parallel, and there we read on "goods and food". Thus the possessions were agricultural. Tithing is an ancient practice, predating the Levitical priesthood, though even in Gen 14 the tithe does support a priesthood (Melchizedek's).

2. Genesis 28.22
Here Jacob promises 10% to God. To whom is he to pay the tithe? In whose support? Presumably it's a tithe on animals & crops. Jacob specialized in livestock, according to Genesis.

3. Numbers 18.21
The tithes supported the Levitical priesthood. This is an important consideration. For example, what if we started a church in a country where no full- or part-time workers were permitted to operate? Of course we'd keep helping the poor, but what about the tithe? Are we prepared to stand behind a blanket tithe as an absolute principle?

Interestingly, a 10% tithe would work well in our full-time worker support plan. 10% on members' gross income would have to cover not only ministers' salary but also benefits, business expenses and employer's taxes. That would probably facilitate a staff to member ratio of 25 or 30:1, which is better than average for our movement the world over. But practicality is a poor argumentation for biblical authority!

4. Numbers 31.28-30
Here spoils of war are assessed. 2% is to go to the Levites (not the usual 10%), and surprisingly only 1/5% to the Lord! That makes a total of 2.2%. So we see the 10% rule is waived in a case of "income" over and above the normal level. How does this fit with our teaching on tithing? Certainly we see this much: the tithe is not an absolute rule on all income.

5. Deuteronomy 12.17
The Israelites were told to eat their tithe (grain, wine, oil & firstborn animals) and freewill offerings. We must admit it would be hard to "eat" our modern "tithe"!

6. Deuteronomy 14.23
To complicate matters further, take into consideration that a sizeable part of the tithe came directly back to the giver! And it was no mere intangible benefit! So would we be allowed to "consecrate" some of our own contribution and use it to buy food and wine (Deut 14.25-26) in the name of God?

7. Luke 18.12
Here the boasting Pharisee claims to give a tithe on everything he gets, not just produce. My question is: Does this show that the tithe was more than just agricultural? However, as we see, the Pharisee also fasts twice a week, so to look for a rule on broad-based tithing here leads logically to a rule on bi-weekly fasting! Many leaders point out that in Matt 5 Jesus says our righteousness must exceed the Pharisees'. And yet if this means we must exceed their tithe, then we should be fasting at least three days a week, too! At any rate, we should be wary of taking the Pharisees' habits as guidelines for our practices, as Jesus warns us in Matt 23.3.

8. Luke 21.1-4
Sacrifice is relative, and Jesus commends someone who clearly gave well over 10%. I have no problem with 10% as a suggested minimum. But to say it's the command of God, or to be hardline about it, gives me problems. At any rate, there's no suggestion in this passage that the givers were tithing.

New Testament Jews gave in at least 5 different ways: Roman tax (Luke 20.25), Temple tax (Matt 17.24), agricultural tithes (Matt 23.23), almsgiving (Matt 6.2), freewill offerings (Lev 7.16, 22.18). Was the total supposed to add up to 10%? At least!

Should we keep giving sacrificially? Absolutely yes! Are we commanded to support our leaders? Yes! Gal 6.6, Matt 10.10 and other verses make that clear. But is there a fixed amount God wills we should give? The burden of proof is on those who would extend the Old Testament's agricultural tithe to total income today. When we do that, it seems to me we're "going beyond what is written" (1 Cor 4.6).

My study of the New Testament leads me to the following conclusions:
* There is no maximum level at which we ought to be giving our contributions. On the other hand, there is no minimum level at which we ought to be giving, either.
* Legalism is a temptation where it pertains to contributions.
* Giving is to be liberal, ungrudging, and sacrificial. In my opinion, most of our first world members -- above all in the United States -- can afford to and ought to give over the 10% level.
* In all things, we are to honor God with our wealth (Proverbs 3:9). That is the heart of the matter.