After lots of testing, the hit online video site Hulu today launched its Hulu Plus pay service for $7.99 per month.

The price is $2 less than originally planned and undercuts, by a dollar, the entry cost of Netflix, Hulu's biggest competitor in the market for streaming premium video content.

Since 2008, Hulu has streamed current and past TV shows and movies to PCs free, a service that in October drew nearly 30 million viewers who spent an average of 208 minutes on the site, according to comScore.

What differentiates Hulu Plus is the availability of full seasons of current TV shows, such as "Glee," "Modern Family" and "The Office," provided by the networks that started Hulu. It's now offering more than 240 seasons of TV shows with 2,400 episodes.

The availability of network shows has made Hulu a useful service for consumers moving away from cable TV services, although the free version of Hulu may lose some of its appeal if the site moves more premium content behind its pay wall.

Hulu is taking its time with the Plus launch, though. For now the premium service will only be available on streaming media devices made by Roku (shown above) and Sony's PlayStation 3 game console. The company said that covers more than 50 million devices in the U.S.

It's aiming to be as ubiquitous on Web-connected TV devices as Netflix. Hulu Plus will be available "in the months to come" on the Xbox 360, TiVo Premiere DVRs and Internet-connected TVs and Blu-ray players made by Vizio, LG and Panasonic.

Hulu Plus is also coming soon to Western Digital's WD TV Live Hub Media Center and WD TV Live Plus Network Media Player.

Later, it's coming to mobile phones, tablet computers and additional devices.

Here's a list of devices supporting Hulu Plus.

Hulu's management team includes a number of veterans of Amazon.com, Microsoft and other Seattle tech companies. It's based in the Los Angeles area but is opening a Seattle office this year.