A division of Lucent reckons they'll have a 300Gb "holodisc" on sale this year.

The name "holodisc" isn't really accurate but in a nutshell, this is how it works:

On a normal disc (CD or DVD), the data is burnt as a series of pits in the surface of the disc representing 1's and 0's.  On the new "holodisc", the data is written at various levels inside the disc itself.  A CD or DVD drive can only write one layer of the disc but the new drives will feature lasers that can vary their angle and intensity allowing them to write at multiple levels within the disc.  It doesn't burn through the other layers because it combines multiple lasers with beams too weak to burn the disc but where the two beams meet, that point is sufficiently strong enough to burn to the disc.

No idea of the costs but ... 300Gb on a CD-type disc?  That's pretty impressive.