What is the best django model field to use to represent a US dollar amount?

The other answers are 100% right but aren't very practical as you'll still have to manually manage output, formatting etc.

I would suggest using django-money:

from djmoney.models.fields import MoneyField
from django.db import models


def SomeModel(models.Model):
    some_currency = MoneyField(
        decimal_places=2,
        default=0,
        default_currency='USD',
        max_digits=11,
    )

Works automatically from templates:

{{ somemodel.some_currency }}

Output:

$123.00

It has a powerful backend via python-money and it's essentially a drop-in replacement for standard decimal fields.

A decimal field is the right choice for the currency value.

It will look something like:

credit = models.DecimalField(max_digits=6, decimal_places=2)