You can still swap out the stock HDD for a bigger one. You can find a 500 GB HDD online for about $100. This 250GB model is likely to be exactly that much more expensive than the 120GB. But for the same price, you can just buy a launch Slim, and have double the HDD space, if you so desire it.

Supposedly they streamlined the swapping process, less super easy to strip screws to go through. Either way, this is great timing. My 360 is acting up again, I can trade it in for credit towards a newly affordable PS3.