[R] Barplot: annotations at tips of each bar?

[tsunhin wong]

Dear R-users,

I have searched through examples of barplot in R.
But there seems to be no advanced annotation options in R for their barplot.
What I am trying to do is to do some annotations at the tip of each
bar in a barplot, similar to the graph below:
http://www.lakesuperiorstreams.org/understanding/images/parameters/king_barplot.gif

What method(s) do you use for these annotations?
Am I going to do some text-overlay on graph mainly?

Thanks a lot!

- John