The DP2 or the wide angle DP1s (better for landscapes) will give the best results (in good shooting conditions) but will also be the fussiest cameras to work with (their menu systems and poky autofocus are rather notorious). They also lack image stabilization and have the slowest lenses of the cameras you list, meaning you won't be able to hand-hold them in poor light conditions that the other two will allow. Of course, they have fixed focal length lenses, not zooms.
The DPs are niche products a bit like very compact view cameras--cameras that reward careful and contemplative shooting but not designed with capturing fleeting "decisive moments" in mind. If you go this route make very sure the tool matches your shooting style.
I don't have S90 experience but it's quickly become a very popular camera with some demanding shooters, so I'll give Canon their due (I've bailed on their G-series). It's reputed to be noticably quicker than the LX3, which can be an important consideration. The 28mm equivalent lens is not nearly as wide as the LX3's but it does zoom further--horses for courses. I prefer landscape shooting, which is further enhanced by the LX's variable aspect ratio.
That they're both f:2.0 and have good IS systems is important for maintaining low ISOs and getting the best output from their small chips (it's easy to envision a scenario where one has to shoot the DP1s at ISO 800 where they could shoot the LX3 at ISO 80).
I'd also consider the S90's lack of a hotshoe, useful not only for mounting a flash but also a viewfinder. Not a big deal to everyone but I use it for both and would miss it.
You've gotten a good response on the oddball Foveon sensor, which defies direct comparison to the common Bayer sensor. It's capable of very good output, no matter how one counts the pixels.
Final thoughts: none of these is a "beginner's" camera, but the Canon and Panny will give good results with their full automatic modes, then reward the learner who digs into the modes and menus and masters the controls. I don't think I'd recommend the Sigmas to a true beginner, as they require some mastery to give good results. You might also want to give the Ricoh lineup a look. The GX and GRD models paved the way for all of the cameras we're discussing here, and are worthy alternatives to them all.