I've built the equivalent to most of the plyr and reshape/reshape2 packages inside pandas (http://pandas.sourceforge.net, note I am in the midst of overhauling the documentation for the upcoming release). I plan to write a decent amount of side-by-side code comparisons, should definitely be useful for folks with R experience wishing to use Python for data analysis / statistics. Feedback from savvier R users than myself on pandas would also be extremely helpful.

Building a plotting library with the ease, sophistication, and beauty of ggplot2 in Python would be a big deal. A number of people I know are interested in venturing down that path (ggpy, anyone?).