Wireless – Cheapest Way to Wirelessly Transmit Video

First of all, the comment regarding your intended application is very important. For this answer, I'm going to assume the you want the highest data rate possible (i.e. Wii-type controller that sends near-instantaneous data). I give you two options below. In both cases, the receiver is simple: receiver board (either another XBee or the sister board of the transmitter you are using) connected to a USB-serial converter connected to your computer.

Option 1: Really easy to build, not-so-low power

An XBee 1mw Chip Antenna can be configured to transmit at whatever datarate you need, has a max. range of 100m, and, best of all, has six on-board ADCs. You can configure the XBee to automatically sample these and transmit their values. X, Y and Z from the accelerometer can go directly into AI0, AI1 and AI2 pins on the XBee and they can both be fed with 3.3V.

• Good: You only need a battery, the accelerometer and the XBee to transmit, and another Xbee to receive.
• Bad: The XBee has 45mA peak current when transmitting.

Option 2: Not so easy to build, low power

The transmitter board you mentioned can be powered by 3.3V (according to the datasheet). Alternatively, you could use this 2.4GHz transciever. In both cases, you will need a microcontroller (easy) or an ADC with serial output (harder, will need a PCB, something along the lines of the MAX1245) to convert the analog signals from the accelerometer to digital signals for the transmitter. I recommend you use a microcontroller (Arduino Pro Mini 3.3V for prototyping, then just an ATMega328 when you're done with the design).

• Good: Low power (7-10mA).
• Bad: Will cost a lot more design time and burnt fingers.

Option 3: Stereo FM transmitters modulating 3 channels of data

This is in response to "Can I do it without converting the signals?".

1. Use resistors and op-amps to bring the accelerometer's readings down to 90mVrms.
2. Use two of these stereo FM transmitters, hook up X to Rin, Y to Lin, and Z to Rin of the other transmitter.
3. Configure the transmitters to Tx on different frequencies.

On the receiver side:

1. Aquire the FM signals and demodulate back to right and left audio. You could use something like this.
2. Amplify and offset the three channels (right and left channel on one, and only right on the other) to measurable voltages (op-amps would work, but I have a feeling we just added a ton of noise to the whole thing).
3. Plug these signals to any microcontroller (Arduino, if you're feeling lazy) with ADCs and send them out as serial data to your computer.

NOTE: Most FM tuners will have band-pass filters that will screw this whole idea up.

The application SOUNDS so trivially simple that, if it isn't, there is no way to know due to the "death by 1,000 blows" approach to defining the problem. At 30 cm the way to use RF is to use RF. Any RF equipment that I have ever met would work over that range in free air in the absence of metal. You can buy transceivers and transmitter / receiver pairs. With the stated specs, if it transmits and receives RF it will be suitable. If any RF data transfer solution does not work in this context then it is because the spec is inadequate. Simple RF solutions usually have minimal latency once the data stream is synchronised. All that is required is Sync_phase - delay_until - sync_now. QED. Repeat as needed. Processor helps BUT a cheap no processor solution is easy.

More complex RF systems such as Bluetooth will also work but may have variable latency. This can be overcome by some interactive communications that establishes link parameters OR designed around known performance. BUT simple cheap off the shelf one way RF modules will work well enough. "ASK" transmission is probably fine and gives you something to search for.

This $5 receiver {315 MHz version} or 434 MHz version

plus this $4 transmitter or its up frequency cousin

will together give you a $9 solution if you are happy to talk one way.
Double that for 2 way.

Or

Two of these $7 transceivers - 434 MHz will give you a bidirectional $14 solution. ~ 16mm x 16mm x 4.2mm.
That size is known OK as the spec did not specifiy otherwise when all details were provided.
That cost is known OK as the spec did not specifiy otherwise when all details were provided.

Datasheet
Programming guide
eXCELLENT APPLICATION GUIDE
mORE OF THE SAME - MANUFACTURERS HOME PAGE {PROBABLY}
rfm12 LIBRARY

Two of these give you a WiFi link - over over over kill.

• BUT

In the absence of any real clues as to why the following are not suitable, the following may be suitable:

• IR may work well and easily and cheaply.
  Unless you are an IR expert, your reasons for excluding it may well be unsound.
  With what you have told us so far, IR would be the candidate solution of choice.
  Low cost, easy, low power. ie
  Better, cheaper, faster - choose any three!
  Tell us what you want and we'll tell you what you need :-)

• Electromagnetic "RF LIKE" "near field" coupling may or may not suit better than RF. .

• Optical

• Acoustic

• Capacitive

• ... GSM ... Iridium ... Inmarsat ... [just joking] :-) .

Pleased explain clearly & completely the environment and relevant constraints. eg:
Potted in concrete, welded in a mumetal drum at the bottom of a shallow shark pond ... :-).
Indoors, outdoors, ... .

There are many "obvious" solutions that may or may be suitable BUT as you do not explain your real need nobody can tell*.

Again: Tell us what you want and we'll tell you what you need :-)

IR sounds good to me, so far.