Atmel have announced a new RF IDIC chip, the ATA5577M1. This 100-150kHZ RFID device is a tiny 2mm x 1.5mm x 0.37mm, using the XDFN package. As the package has an internal 330pF capacitor, it requirs only an external antenna coil to form a complete LF-RFID tag.
This device is available for sampling now, with pricing starting at $0.38USD for 20k quantities.
For further details, see here.