A while back, Jeremy Ritter asked the yt-users list if yt could produce a particle plot like that obtained through annotate_particles(), but without loading any mesh data. The answer was "no", but that it isn't too hard to use matplotlib directly. Personally, this is a visualization task that I do all the time, and I think it would be useful to make this type of plot a one-liner in yt - provided it handles units and labels and such automatically like any other yt plot.
I've added this feature in my fork of yt. The interface is the same as for any other yt plots, and the standard plot modification mechanisms should work. Examples are here http://nbviewer.ipython.org/gist/atmyers/f8616c9ed5a9d2b027e8... and here http://nbviewer.ipython.org/gist/atmyers/8d979d990268f48c9688....
If there is interest in having this in mainline yt I'll write some docs and issue a pull request.