It is up to what you want to watch and how much space you have in you TV cabinet. The most flexible way is to connect a Home Theatre PC to the TV, so you can watch anything. If you have Netflix and sometimes play games, Netflix instant watching is available on PS3, XBOX and Wii. Another solution is the networked media players, such as WD TV Live, which can play YouTube video (Different network players may have different capability with online content). And to get more online content, you may set up a Media Server to stream online video to the media player.
A very inexpensive solution is to purchase a laptop with a broken screen from eBay. Remove the screen and connect the monitor output to your TV. Simple, cheap, and best of all: very low power consumption so you don't have to power it on every time you want to use it. Combine this with a wireless keyboard and mouse (I use the DiNovo mini).