The Foveon sensor is newer than both CCD and CMOS, but has been around for a few years.
Low-light performance is not it's forte and many reviews of the Sigma cameras with this sensor suggests that this sensor isn't particularly good at ' high ISO. However, the processors' performance is also part of the equation.
Where the Foveon appears to excel is with regards to color and the amount of detail a good color pickup can generate. As this sensor captures RGB info at all photo sites, it is claimed to be able to generate more detail on a number of conditions.
CCD and CMOS use the Bayer interpolation to "guess" the correct color of each pixel although each photo site can only pick up either R, G or B.
A very interesting article by Mike Chaney can be found here: http://www.ddisoftware.com/sd14-5d/
It's about the best and more thorough coverage of the Foveon sensor I have read so far and I am very excited to see how the recently announced Sigma SD-15 camera will perform.