Some TVs have Wi-Fi support (for example, Sony Bravia KDL-40NX700), so you can connect them wirelessly.

You can also use a network media player with Wi-Fi support (like WD TV Live HD Media Player) to connect your computer to HDTV wirelessly. You will also need a DLNA server software (such as Windows Media Center).

See also:
How to connect PC/computer/laptop to TV (wired connections)