I remember in one game I played the DM used Adobe software to make the kewlest maps I'd ever seen. Adobe stuff's expensive though, unless you have 'other means' of getting it. Other things I've seen done is making a map on paper (usually the kind covered in squares, for mathsy stuff) and scanning it, or just making a basic one with text:
eg.
1 2 3 4 5 6 7 8 9
a
b
c
d
e
f
g
h
i
Not very nice to look at but it works in a bind.