surely "closest" dates are also future dates??
And is today a closest date, a past date or a future date?
Assuming that the date field is called date_field and the table is called
SELECT date_field FROM date_table WHERE date_field > NOW() ORDER BY
SELECT date_field FROM date_table WHERE date_field <= NOW() ORDER BY
you may need to play around with the where clause depending on the answer to
one of above questions.