models.py

class Foo(Model):
    bars = ManyToManyField(Bar, related_name='foos', blank=True, null=True)

class Bar(Model):
    name = CharField(unique=True)

# The process I know currently:
foo = Foo()
foo.save()

bar1 = Bar.objects.create(name='bar1')
bar2 = Bar.objects.create(name='bar2')

foo.bars.add(bar1)
foo.bars.add(bar2)

# What I would like to do
foo = Foo(bars=['bar1', 'bar2'])
foo.save()