There is a pretty full range of Sigma compacts of different generations.
The original 4.7MP: DP1, DP2
The next generation "S" versions (also 4.7MP)
The third generation "x" versions (also 4.7MP)
The 15MP Merrills: DP1 Merrill, DP2 Merrill, DP3 Merrill
The 19MP Quattro range: DP1Q, DP2Q, DP3Q and recently the DP0Q.
Within each family, they tend to be the same apart from lens. The DP1 has a fixed 28mm equivalent lens, the DP2 a fixed 41 (45mm in later models), the DP3 a 75mm equivalent. The DP0Q has a 21mm equivalent.
The Merrill and Quattro sensors are 1.5x crop sensors, the original 4.7MP sensors were 1.7x crop.
Outside the compacts, the SD9 and SD10 DSLRs have first generation Foveon 3.4MP 1.7x crop sensors, the SD14, SD15 have the 4.7MP 1.7x crop sensors and the SD1 has the 1.5x Merrill sensor. No DSLRs as yet are using the current Quattro sensor.
All models come with SPP raw conversion software. The earlier models (SD9,10,14; DP1, DP2) are supported by Lightroom.
The early DP cameras with the 4.7MP sensors obviously don't have the resolution of the Merrill's and Quattros but lots of people were fans of the image quality at base ISO. Very sharp whilst being smooth and relaxed at the same time -which sounds like a contradiction but makes a lot of sharp Bayer pictures seem over-processed.
All Sigmas are rather spartan and slow to use.
I have owned a DP1 for a while and love it. Recently I bought a used DP2 from a Japanese eBay retailer.
The controls, menu and battery are totally different from the DP1. I looked up the user's manual online and found two versions of the camera - one just like the one I just bought and one just like my DP1. Anyone know what gives?