what your budget is. Assuming you don't want an 'L' lense, the 17-85mm IS USM is a fairly good choice. It will go reasonably wide, and can pull in a modest distance if zoomed. It takes good pictures although they can be a touch on the soft side. Sharper and faster lenses are available, but are priced substantially higher.
for amatuer (sp) photog--lots of baby pics--close ups---what is another lens to have?