Digital media device maker Roku announced today that it scored an undisclosed but substantial amount in third round funding. Famous for the Netflix Player — the set-top box that lets you watch any of Netflix’s “play instantly” movies or TV shows in your living room — the Saratoga, Calif. company plans to use the new money to further develop its flagship product and others that stream digital media to the TV.

Menlo Ventures provided the round, which comes less than a year after financing from Netflix in January. The goal now for the young company is to edge out its rivals in the field, including Apple TV (which delivers digital television to your computer or TV set), and Vudu (which streams movies). And while Microsoft is still working on launching Netflix “play instantly” fare on the XBox 360, it will pose a serious threat when it does. Yet, despite the formidable competition, the company says there are no plans to sell to a larger player.

As we reported earlier, Roku’s success may depend on its ability to strike partnerships with other digital content providers that may interest general consumers. Amazon’s Video On Demand and NBC’s Hulu would give Roku a major advantage. When asked, a spokesperson said the company is looking to distribute advertising-supported content, in particular, as well as user-generated content in the near future.