I am going to assume that your intended purpose for a "computer to TV transmitter" is to stream video that is stored on your computer to a TV for display.
Here are just a few of the products you can use:
1. most Blu-ray players can be connected to a home network (which your computer could be connected to wirelessly), and will display a video data stream sent from your computer.
2. most gaming consoles (like the PS3 and XBox360) can be connected to a home network (which your computer could be connected to wirelessly), and will display a video data stream sent from your computer.
3. the Apple TV device
4. the Western Digital "TV Live" product line of network media players
5. the D-Link "Boxee Box"
