SDL 2.0 (a.k.a. "SDL2") has been in development for many years and has many new features should finally be out as stable this week.
Sam Lantinga, who joined Valve Software to work on Steam for Linux, has been hard at work with Ryan Gordon and others on delivering this new release. SDL 2.0 has already come to play an important role at Valve Software and their Linux efforts.
SDL 2.0 has new features like hardware-accelerated 2D graphics support, new render targets, multiple windows support, much better audio support (up to 7.1 spealer output), multi-touch input API support, multi-threading improvements, and a hell of a lot more. SDL 2.0 is really great for game/application developers. Another important change for SDL 2.0 is that it's published under the zlib license. Under this more permissive license over GPLv2 in SDL 1.2 is that it allows for it to be statically linked within commercial closed-source games.
Sam Lantinga announced this past Saturday the final SDL 2.0 release candidate. With this final 2.0 RC he noted, "We have the final SDL 2.0 RC builds up for testing over this weekend, and we'll be releasing next week!"
Ryan Gordon also wrote on Google+ about his latest SDL2 work.