This month, Xbox 360 owners with overburdened hard drives will have a relatively cheap opportunity to stock up on extra space. That is to say, it's relatively cheap for an Xbox 360 HDD. Relative to any other HDD, you're paying out the ears.
Still, if you're a hard drive power-user you might want to consider this upgrade when it releases next month. Especially if you, or someone you know would be interested in using the included free LEGO Star Wars III: The Clone Wars code that's included with the offer.
Note that the hard drive is only compatible with Xbox 360 S models.