How can I turn my iPhone into a tv remote control?

Which software/hardware can turn my iPhone into a decent remote control for my TV?

(Are there any reviews out there that compare the options?)

You'll need an IR dongle (the iPhone doesn't natively have any IR capabilities). Google for iPhone IR remote and you'll see several options.

Some of the new internet-connected TVs can be controlled via WiFi using apps available in the App Store. Here's an example for 2010 model Samsung Internet@TVs.

The Griffin Beacon looks like it should do what you want. It combines an iPhone app with an IR emitter that you place on a table and control via Bluetooth.