Antec 300 comes with one rear 120mm fan, and one top 140mm fan. It has two additional front bays for 120mm fans, but does not come with any. I recommend Antec TriCool fans, it will match what the case comes with so you won't have any difference in the hum of the fans - so your computer will sound quieter.
Like dtemple said, it comes with 1x120 rear and 1x140 top. You definitely want to put at least 1x120 in the front, so that you have a nice strong airflow through the case.
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