As of writing the article this morning in the US, there's 1,002 games available for SteamOS + Linux as shown here. If including other software and demos/DLC, etc, there's 1,853 items available natively for Linux.
The newest Linux titles to the Steam store are PAYDAY, Hotline Miami 2, Cities: Skylines, and Parallax. The highest-priced Linux software on Steam is the Wing IDE 5 Commercial version for $120 USD, which is actually a programming IDE, or if just counting gasmes it is Borderlands: The Pre-Sequel at $60.
It was less than one year ago that Steam crossed 500 Linux titles. It's been three years to the month since Gabe Newell approached me about their Linux work that led to the original unveiling of big Steam for Linux news. In my most recent email from Gabe last week, he confirmed remaining very bullish on Linux, which shouldn't come as any surprise given their announcements from GDC of developing an Intel Vulkan GPU driver, Steam Machines launching in November, etc.
These 1,000 titles for Linux while Steam on OS X has 1,609 titles and overall there's 4,804 games on Steam. The Steam Linux market-share remains just around 1.0% with no big shifts in the Linux gaming landscape expected until later this year when Steam Machines start shipping and SteamOS becomes more enriched.