The nice cable operators use modems with RJ-45 outputs (to my knowledge, anyway), so any wireless router will do fine for you.
Good brands are Linksys, Belkin, Netgear, and a few others.
This is one such example as something suitable. Any device that wants wireless access will also need an adapter plugged into the back of it.
This package includes one for you, or you can just buy them
separately. Note also that many laptops now come with wireless built-in, so your wife's laptop may not need one.