The digital cameras which I currenlty use are:

Samsung GX-10
Ricoh GX-100
Pentax *ist-ds

A comparison between the currently available DSLR camera sensors

sensor size comparison

35mm sized sensors are found in the top-line pro bodies of Nikon, Canon and Sony.
A 50mm lens is considerd a "normal" for this sensor size.

The APS-c size is currently being used by Nikon and Sony in their "entry level" DSLR cameras
and by Pentax and Samsung in all their current DSLR cameras.
It has a "crop factor" of 1.5x and this means that the sensor is 2/3 the size of a 35mm frame
and lenses appear to have their focal length increased by 50%.
A 33.3mm lens would be a "true" normal lens focal length for APS-c
With this sensor size 28mm, 31mm and 35mm focal lengths have been mooted as a "normal" focal length,
with no agreed to standard yet.

Canon APS-c is the size used in all their "entry level" DSLR cameras and has a "crop factor" of 1.6x.
A lens mounted on a Canon APS-c DSLR camera appear to have it's focal length increased by 60%.
A 31.3mm lens would be a "true" normal lens focal length for Canon APS-c.
The closest lens made by Canon to a normal is their EF 35mm f/1.4L USM.

FourThirds is used in Olympus and Panasonic DSLR cameras and in their Micro FourThirds EVF cameras.
Leica has some of the Panasonic DSLR cameras rebranded as part of their Digilux range.
It is roughly 1/2 the size of a 35mm frame and lenses for this sensor size appear to have their focal length increased by 100%.
Leica makes the LEICA D SUMMILUX 25mm/F1.4 ASPH which (at the moment) is the only normal available for this sensor size.

Resolution Test

This is a comparison of what an image looks like when resampled to lower resolutions.

The left hand column is a crop of the cartoon in the top left hand corner of this newspaper page.
For each version, I resampled to the target resolution and then cropped down to the cartoon, trying to sample the same area in each.
From top to bottom, the crops are of 6mp, 5mp, 4mp, 3mp, 1.3mp, 800x600 and 640x480

The original imagewas taken with a KM Dimage A200 at full 8mp resolution on the "extra fine" quality jpeg setting.
No sharpening was done to the original or to any of the resampled versions.

original 8mp

cropped from a 6mp version
6 megapixel

cropped from a 5mp version
5 megapixel

cropped from a 4mp version
4 megapixel

cropped from a 3mp version
3 megapixel

cropped from a 2mp version
2 megapixel

cropped from a 1.3mp version
1.3 megapixel

cropped from a 800x600 version

cropped from a 640x480 version