Here's my submission.
def PowerSet(base):
power_set = []
b = len(base)
map(lambda g: power_set.append(map(lambda x: base[x],
filter(lambda x: g[x], range(0, b)))),
map(lambda value: map(lambda x: (value >> x) & 1, range(b - 1, -1, -1)),
map(lambda value: value ^ (value / 2), range(0, 2**b))))
return power_set
print PowerSet([1,2,3])
This definitely won't win for readability but it's the shortest I could come up with.