The cheap 18-55mm lens that comes with the EOS Ds
normally isn't sold by Canon apart from with the camera
bodies. It's a cheap lens and you could probably pick
it up for next to noting on Fleabay.
It depends on what you want to take pictures
of mostly. For landscapes normally you need wideangle
so would go for a zoom with ranges below 50mm
and for things requiring telephoto you aim for lenses
with zoom ranges above 50mm.
The next thing to consider is money. You could
spend loads on a great lens, but as you've opted for
an older budget camera you probably don't want to
spend more than a few hundred.
Check out the Canon EF-S 18-55mm (F3.5-5.6) IS lens
Amazon.co.uk: Canon EF-S 18-55mm f/3.5-5.6 IS Lens: Electronics & Photo
And also EF 28-105 (F3.5-4.4) USM
Amazon.co.uk: Canon EF 28-105mm f/3.5-4.5 II USM Zoom Lens: Canon: Electronics & Photo
Canon lenses can be image stabilised (IS) and USM means
they have ultrasonic motors for focus. (Smoother, less noise)
The EF-S (As opposed to standard EF) are lenses that
have been designed specifically for digital camera bodies
instead of film. There are things to consider but basically
Canon have been able to make them more compact due
to the smaller size of the image sensor compared to 35mm film.)
The stabilised lenses mean you can go use
them in slightly lower light or with slightly lower shutter
speeds without resorting to a tripod.
They do not have powered zooms.
Another option is to go for someone like Sigma,
e.g.
Amazon.co.uk: Sigma 55-200mm AF F4-5.6 DC Digital Lens for Canon AF Mount: Sigma: Electronics & Photo
Amazon.co.uk: Sigma 18-125mm AF F3.5-5.6 DC Digital Lens for Canon AF Mount: Electronics & Photo
Amazon.co.uk is good for reference but you don't have
to buy them from there. Shop around.
I use the standard 18-55mm lens and the Sigma 55-200mm
which aren't top notch lenses but are adequate
for what I do. If I was buying another it would be an IS
Canon zoom.) Probably
Amazon.co.uk: Canon EF - Zoom lens - 28 mm - 135 mm - f/3.5-5.6 IS USM - Canon EF: Electronics & Photo