There are two major types of digital video services available today, a la carte offerings like iTunes Store that offer movies and TV shows for purchases and rentals, and video streaming services like Netflix. Interestingly, only Amazon offers a truly viable alternative in both markets, and this week the online retailing giant announced an improvement to its selections in both areas.

According to Amazon, the company now offers over 100,000 movies and TV shows for purchase or rent via its Instant Video service, over 15,000 of which are available in HD. And it provides over 9,000 movies and TV shows for streaming; best of all, subscribers to the company's Amazon Prime service get this streaming functionality for free.

Like Netflix, Amazon Instant Video--which again offers video rentals and purchases as well as streaming--is available via numerous set-top boxes and other digital devices, including PCs, Macs, and over 300 televisions, Blu-Ray players, and set-top boxes.

Why is this important? While the market for a la carte video appears to be up for grabs--Apple's iTunes competes with similar services but also with cable companies' On Demand functionality--the suddenly lucrative streaming video market has only one major player right now. That's Netflix, thanks largely to the decline of Hulu Plus, which has turned into a low-rent, TV show rerun service. So Amazon sees a chance to unseat Netflix, which of course recently angered subscribers with a pretty serious price hike.

As a subscriber to Amazon Prime, I like that Amazon's Instant Video streaming service is free. But the selection is still pretty lousy compared to Netflix. I expect that to change over time. For now, however, I'd just recommend keeping an eye on Amazon to see how this improves. And yes, if you're already paying for Amazon Prime, by all means check out the free streaming service. But it's not time to replace Netflix. Not yet.