First thing to be addressed is what do you wish to do with the additional
lens? Do you need the mm's? Do you need the wider aperture? Do you need VR?

Hunt

Formally the complementary lens to any of the
major makers' 18-55mm is their unjustly overlooked
55-18mm lens.

You'll likely appreciate the extra reach of the 70-300s but I saw a
test recently (with them and then a good lens, the Olympus
50-200 which acts like a 100-400 on Olympus 4/3rds systems) and the
Olympus literally slaughted the cheap ones when it came
to resolution.  The difference was so graphic you could easily see it
in a magazine's tiny reproduction. But the big question is, can a
really good 70-200 match a 70-300 when it comes to printing a picture
at the same size, given fewer  pixels will be in any given
area of the 200mm shots.  From what I saw in the test, yes, if that
high end lens is really that much better.  Plus, you do get an extra
stop.  What I would do is go to a store (if possible) and test them out
with your camera body.  It's the only way to be sure.

Go to eBay and look around.  After I bought my DS I caught lens fever and
before long had bought FOUR (yes FOUR) lenses of that type... 2 by
Pentax, 1 Tamron and 1 Quantaray (Sigma).  All were rather cheap, and
each has different characteristics which I appreciate.  The Tamron is
incredibly short, the Sigma is light but very sharp (though zooming
requires re-focus), one Pentax has internal zoom and is very light but
soft in corners, the other is far longer and heavier, but sharper.

None cost more than $50, including shipping. All four are worth the
money, and dropping or losing any one of them would _not_ give me a
heart-attack.

eBay has equipped my Pentax with usable glass from 16 to 500mm.

Lenses don't take photos... photographers do.