Use the bar function to make bar charts: http://matplotlib.sourceforge.net/matplotlib.pylab.html#-bar
Here's an example script that makes a bar char with error bars and labels centered under the bars.
#!/usr/bin/env python
import numpy.numarray as na
from pylab import *
labels = ["Baseline", "System"]
data = [3.75 , 4.75]
error = [0.3497 , 0.3108]
xlocations = na.array(range(len(data)))+0.5
width = 0.5
bar(xlocations, data, yerr=error, width=width)
yticks(range(0, 8))
xticks(xlocations+ width/2, labels)
xlim(0, xlocations[-1]+width*2)
title("Average Ratings on the Training Set")
gca().get_xaxis().tick_bottom()
gca().get_yaxis().tick_left()
show()
