Earlier today, I responded to an R-sig-phylo request to be able to plot bars showing phenotypic trait values for species at the times of a circular or 'fan' tree. I have now added this function (plotTree.wBars) to the phytools package. It can be downloaded & installed from source here.
In addition to plotting a circular tree, this function version also:
(1) Plots a square phylogram in "rightward" or "leftward" orientation.
(2) Plots a stochastic character mapped tree (using plotSimmap instead of plotTree internally).
(3) Can accept most of the arguments of plotTree & plotSimmap (see the documentation page for plotSimmap for more information.)
Here's a demo:
> plotTree.wBars(tree,x,method="plotSimmap", colors=setNames(c("blue","red"),1:2),lwd=3)