There are of course many products that will do what you need, but to get you started.
Wireless Routers (Plugs into your existing modem to provide wireless connectivity):
D-Link DI-524
Netgear WG602
Powerline (Allows transmission of data via the household electrical wiring):
D-Link DHP-301
Netgear WGXB102
In my experience though it is often cheaper to buy an all-in-one modem/wireless router.