As expected, iTunes 10 has added to the TV show purchase model and is introducing rentals. It'll cost you a buck for an HD episode, and $5 to watch first-run movies in HD. Crucially, those movies will be available on the same day as their DVD counterparts. You'll have 30 days after you rented to watch, and 48 hours from when you start watching before your content disappears in a puff of smoke.
All content will be commercial-free, although your range of choice will be a bit limited at first: so far Fox, Disney (and its ABC family of networks), and BBC America are signed up for the ride. Competitive pricing like this is going to be hugely important for AppleTV—on which you can only rent, not buy and store—if it's ever going to grow beyond the niche it's been stuck in since its previous release.