This is an SD card with a twist: it also has Wi-Fi which means that, if you use it with a digital camera, it allows you to send photos you’ve just captured on Flickr, Picasa, Facebook, email them or simply back them up online.
Sounds like a simple & great idea.
The site of the company behind this product is here: http://www.eye.fi/
Amazon is selling the Eye-Fi Pro 4GB cards for about £120 in the UK. http://www.amazon.co.uk/gp/product/B002RL9ALU/
There is a slightly cheaper model, Eye-Fi Share Video, which is also on Amazon for about £70. http://www.amazon.co.uk/dp/B002RL9ALK
It would be interesting to see if this ends up in an Arduino shield at some point. In the mean time, the best Wi-Fi solution for the arduinos seems to be the WiShield.