Kit lens like 18-55 definitely can be used, especially when u shoot with flash. Have shot before with Canon's equivalent for a friend's wedding and they loved the pics. But it does limit ur creativity though and it's difficult to take pics with shallow depths of view (e.g. selective parts of the photo in focus). Also, the "smoothness" of the out of focus areas are not as nice as the better lenses.
For the first poster, the best lens for u could be different from another. A lot depends on the shooting style. Usually, u'll want a lens that's wide enough (28mm equivalent after the 1.5x crop factor) cos u'll need to shoot groups of people indoors. As for how tele and how wide an aperture, it'll depend on how u shoot. If u're more interactive with couple and guests and u're close to the action, u'll likely not need a long lens.