In addition to NASA's in-house SLS (see aramis's answer), NASA is sinking a good deal of cash into its Commercial Crew Development (CCDev) program, \$1.5 billion between 2010 and 2014.
What is CCDev?
CCDev is essentially "son of COTS" (Commercial Orbital Transportation Services). COTS was a remarkably successful program. For a mere \$800 million, NASA has two new vehicles at its disposal for delivering cargo to the International Space Station. The goal of CCDev is to continue the spirit of the COTS program, but this time with a goal of putting humans into space.
The first phase of the project, CCDev1, involved \$49.8 million spread amongst five companies: Blue Origin, Boeing, Paragon, Sierra Nevada, and ULA. The second phase, CCDev2, involved \$315.5 million spread amongst four companies, three of which were in CCDev1. Those three were Blue Origin, Boeing, Paragon, and Sierra Nevada. SpaceX was also selected for CCDev2. The third phase, Commercial Crew integrated Capability (CCiCap) involved \$1167.5 million spread amongst only three companies: Boeing, Sierra Nevada, and SpaceX.
The final part, Commercial Crew Transportation Capability (CCtCap) is expected to be even bigger. The FY14 budget for this final part is \$696 million (cut from a request of \$821 million). The first phase of this final part, CPC1, involved \$29.6 million, spread amongst the CCiCap contractors. How many of those three finalists will receive CCtCap is undetermined. (Note: Any company could submit a CCtCap proposal. However, the three companies that had collectively received over a billion have a huge leg up on any newcomers.) Rumor has it that CCtCap will involve two companies to foster competition, but budget concerns might make it one.
Who's building what?
Boeing is working with Bigelow Aerospace on a new capsule, the CST-100. The Boeing capsule is designed to be compatible with the Atlas V, Delta IV, and Falcon 9 launch vehicles. The initial work is targeting launch with the Atlas V.
Sierra Nevada is working on the Dream Chaser that Sierra Nevada acquired with it's purchase of SpaceDev. The Dream Chaser is the only lifting body left in the CCDev competition. Plans are to have it be launched on an Atlas V.
SpaceX has been working on outfitting its Dragon capsule with life support and making its Falcon 9 launch vehicle human rated.
Addendum (to address comments)
The end goal of CCDev has always been an end-to-end Crew Transportation System. The initial work focused on various parts of that ultimate goal, with most of the funding going toward the vehicles that will dock with the ISS and return to Earth. However, a small portion of the very first chunk CCDev money did go to United Launch Alliance to work toward making their launch vehicles human rated.
The RFP for the final phase of the CCDev program, CCtCap, was released in its final form in November 2013 with a submission deadline of January 22, 2014. All proposals had to be for an end-to-end Crew Transportation System with a manned demo mission in late 2017 (budget pending). The capsule or lifting body is but a part of that end-to-end system. The launch vehicle is another rather important part.
The goals of CCDev and SLS are largely orthogonal to one another. The primary goal of CCDev is to restore the ability of the US to send humans to the International Space Station (ISS) "and other low Earth orbit destinations". The primary goal of the SLS is to restore the ability of the US to send humans beyond low Earth orbit and eventually, outside of Earth orbit. CCDev is not intended to send humans beyond LEO; SLS is not intended to go to the ISS.
The launch vehicle proposed by a CCtCap bidder will not be the Space Launch System (SLS) vehicle. There is a backup plan to use SLS for human flights to the ISS, but only if CCDev fails.
General discussion on CCDev:
Boeing's CST-100: http://en.wikipedia.org/wiki/CST-100
Sierra Nevada's Dream Chaser: http://en.wikipedia.org/wiki/Dream_Chaser_(spacecraft)
Human-rated Atlas V: http://en.wikipedia.org/wiki/Atlas_V#Future_developments
SpaceX's Dragon and Falcon 9: http://en.wikipedia.org/wiki/Dragon_(spacecraft) and http://en.wikipedia.org/wiki/Falcon_9
GSA solicitation page: https://www.fbo.gov/?s=opportunity&mode=form&id=e016cb01d032ec7468ca85035072a43c&tab=core&_cview=0
NAIS solicitation page: https://prod.nais.nasa.gov/cgibin/eps/sol.cgi?acqid=158768
SLS/MPCV as a backup to CCDev: http://www.nasa.gov/sites/default/files/files/Dumbacher_MPCVSLS_508.pdf, slide #10.
SLS as a backup to CCDev: http://www.nasa.gov/pdf/510449main_SLS_MPCV_90-day_Report.pdf
From page 7 of the latter,
The vehicle must be capable of serving as a backup system for supplying and supporting cargo and crew delivery requirements for the International Space Station (ISS) in the event such requirements are not met by available commercial or partner-supplied vehicles.