Rendering Options - Active Jobs:

If you want to stop a rendering job, you can either click the X in the top right of the rendering window (if you are displaying during rendering), or go to Render|Options and select the "Active Jobs" tab.  From there you can click on a particular render job and abort it, or simply abort all the active jobs.

Figure 8 shows the active jobs panel with two rendering jobs (both completed).


Options Dialog Box
Job Control Dialog