command | curl -F "content=@-"

You can add anything after the returned URL, as long as the first character is not a number. A few extensions will actually get the right Content-Type sent along :)

Files with Content-Type support are:

application/pdf  pdf 
image/jpeg       jpg jpeg 
image/gif        gif 
image/png        png 
text/html        html 
text/x-csrc      c 
video/mp4        mp4 
audio/mpeg       mp3