Arduino wireless(short range)

Hi. I am working on a project where i require a really small wireless transmitter(from a proximity detector) and receiver(to arduino). Basically the proximity detector will trigger the transmitter to send to the receiver which is connected to the arduino and then run a sketch.

My main concern is the Tx&Rx must be as small as possible(short distance). Transmit distance is only <1m needed(~50cm to be exact.). RF transmission. preferably easy and able to build one myself or cheap to buy.
i have found some useful info like FM transmitter bug and bunch of others but would like to seek suggestion here. Since i am new to arduino and wireless i hope some of u guys can give me some suggestion/advice.

Thanks.

For such a short range many possibilities exist, from bluetooth to Xbee, but the cheapest is likely to be a serial RF link - there are quite a few options for this, especially if you don't need high bandwidth. It doesn't sound like you'll be troubled by low signal or interference at that range.

this is what I am using, range is unimaginable, I am guessing check your state law before you buying it.
http://goo.gl/7I4AA