There are lots of SLR's popping out on the market today, but the size of the ImageSensor was a bit confusing, i.e. what size do I have on my compact camera?, what is that size compared to SLR's?
This article gives discusses the sizes between fullformat and APS-C which is the common size for SLR's today (consumer, pro-sumer cameras)
This article shows you the differenses for common sensor sizes that are, or has been in use.
So, my camera, an Canon Powershot S60 has something called 1/1.8 inch, and is 7.176 x 5.319mm, compare that to an APS-C, which is about 22 x 15 mm (I see there are some small variations there), and an fullformat imagesensor is an whopping 36 x 24, but that costs an fortune compared to APS-C.