This plot was created with Matplotlib.

The code is (using the python-networkx and python-matplotlib packages on Ubuntu GNU/Linux distribution):

#! /usr/bin/python
# coding: utf-8

import networkx
#import pylab
from pylab import pi, cos, sin, linspace, array
import matplotlib.pyplot as plt
import os 

node_number = 20
initial_nodes = 2
animation = False
animation = True

G=networkx.barabasi_albert_graph(node_number, initial_nodes)

# pos=networkx.graphviz_layout(G, prog="dot")
type="shell4"
pos=networkx.shell_layout(G)
#pos=networkx.graphviz_layout(G,prog='twopi',args=)
print pos

dir=os.path.join("images", type)
if not os.path.isdir(dir):
    os.mkdir(dir)

Ge = networkx.empty_graph(node_number)
#networkx.draw(GG,pos, node_color="w")

for i in range(initial_nodes,node_number):
    nodes = range(i+1)
    GG = G.subgraph(nodes)
    plt.figure(figsize=(8,8))
    networkx.draw(GG,pos, node_color="w", alpha=0.5, node_color="blue", node_size=20, with_labels=False, hold=False)
    #networkx.draw(Ge,pos, node_color="w", alpha=0.5, node_color="blue", node_size=20, with_labels=False, hold=True)
    #nx.draw(G,pos,node_size=20,alpha=0.5,node_color="blue", with_labels=False)
    xmax=max(xx for xx,yy in pos.values())
    xmin=min(xx for xx,yy in pos.values() + [(0,0)])
    ymax=max(yy for xx,yy in pos.values())
    ymin=min(yy for xx,yy in pos.values() + [(0,0)])
    dx = xmax - xmin
    ddx=0.1*dx
    dy = ymax - ymin
    ddy=0.1*dy
    plt.xlim(xmin-ddx,xmax+ddx)
    plt.ylim(ymin-ddy,ymax+ddy)
    plt.savefig("%s/barabasi_%s%02d.png" % (dir, type, i))

if animation:
    input = os.path.join(dir, "*.png")
    output = os.path.join(dir, "barabasi_albert.gif")
    os.system("convert -delay 100 -loop 0 %s %s" % (input, output))

(If someone knows how to eliminate the frame around the network, write to me, please.)

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