What does your TV have for inputs? Would it be practical to put your computer within a couple feet of the TV (ie, do you have a laptop)? Do any of the computer's outputs match up with the TV's inputs? If so, there's a good chance you're one cable away from plugging the computer straight into the TV. Maybe two cables, depending on specifics.
If that's not an option, you'll need something a touch smarter to plug into the TV. PS3 and Xbox 360 should both support media streaming (PS3 link
, xbox link
), so long as they are connected to the same network your computer is. It looks like the Wii can kinda-sorta be made to work, but it's far from ideal.
If you don't have one of those consoles around, either, you'll need to add a device to handle things. Exactly what you need is going to depend a bit on your needs - something like a Roku or WD TV Live type of device would work, or an Apple TV or even a full blown HTPC. Depending on the particular streaming box, it may or may not work over WiFi, but I'd suggest running ethernet if you're at all able to, as media streaming is a little more demanding than web browsing.