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I'd encourage you to explore the PHP 5.3 DateTime class. It makes dates and times far easier to work with:
$tomorrow = new DateTime('tomorrow');
// e.g. echo 2010-10-13
echo $tomorrow->format('d-m-Y');
Furthermore, you can use the + 1 day syntax with any date:
$xmasDay = new DateTime('2010-12-24 + 1 day');
echo $xmasDay->format('Y-m-d'); // 2010-12-25