In OS X Mavericks how do I drag a window to another space? I was able to do this in Mountain Lion.
Go to system preferences -> Mission Control and uncheck "Displays have separate Spaces"
Now logout and login.
You now should be able to drag your windows between spaces like in (Mountain) Lion.
Simply drag the window to the edge of the screen and hold it there for about a second.
The space slides to the side and you can drop the window into that space.
Alternatively, you can open Mission Control and drag the window to an existing space or directly to a new space by dragging it to the new space button in the top right.