Low light/High ISO performance?

If all things are equal with technology in a sensor and they are the same sized sensor, then the one with the lower MP will be better with noise in high ISOs. The problem is that each sensor is different and with different technology and different ways of processing the photos.

For the most part, size of the sensor will make a bigger difference on the noise in high ISOs.

There are a number of cameras that can do great in high ISO with low noise. Some that are considered the best are the Nikon D3s, Nikon D700, Canon 1D Mark IV,and Canon 5D MarkII. Those cameras also need to have a large aperture lens attached. You'd be looking between $3500 and $6500 for one of those bodies and a large aperture zoom lens.

To a lesser extent, there are DSLR bodies that don't do as well as the previous ones mentioned do, but they do very good, for the price. The best low light DSLR for the least amount of money would be the Pentax K-x. You're still looking at over a $1000 for the camera and one large aperture lens.

If that's still too much then you can look at the compact cameras. The Canon G11 and the Canon S90. The difference between the first cameras I told you about and these are very large for noise in high ISOs. It's just what your requirements are, your budget, and how much you're willing to compromise.

In general the D-SLR performs the best in low light/high ISO, compared to compacts and even the medium format cameras. The bigger the D-SLR sensor, usually the lower the noise. Fewer MP will lower the pixel density and increase the pixel size, which also helps. For low light action shots, it is critical to have a fast large aperture lens. For low light still shots, it is critical to have a tripod. Which manufacturer you pick is not going to make a big big difference. You need to be careful to get the right exposure for what you want to capture, this is usually more important than whether you use a Nikon or Canon. But if you are curious which camera fair better in low light, here is a link for some objective testing with ranking of the camera in terms of different performances. Click on the ISO tab and you can see the ranking of the high ISO performance:
http://www.dxomark.com/index.php/eng/DxOMark-Sensor

good camera with less megapixel can be claimed for the low noise shooting outcome. But, that condition disregards many other aspects. The noise of output level varies upon many criteria. For example, correction upon shooting light metering, brighter lense aperture, and camera's hidden hardware and software control.

When shooting at the correct light metering ( not too underexposure ), the noise level is likely to become very dim; The correct light compensating, such as slow shutter speed and wider aperture, allows the camera taking more light amount. But, too underexposure picture will result loosing the beautiful shadow and flatten picture's lighting.

A DSLR with a brighter lense will mostly generate less noise level comparing to the same camera with more F-stop lense. For example, the lense with F4 will have trouble with noise at the dim light more than that of F2. However, some good design lenses do not have to go for the wide aperture to compete for a lower noise. I tested Carl Distagon 35 F2 ZE lense against Canon 35 F1.4L, under the same dim lighting circumstance using the same EOS 5D mark II camera. The noise level picture generated by using Carl Zeiss at F2 is significantly better than that of using Canon F1.4L at the very same aperture.

Most today camera design not only their hardware, but also software. The camera hardware, firmware, and its processor determine how much noise level the camera records, how sharp the details are, how each color appears. For noise issue, it must trade off between what to show details, more noise, and milky details, less noise.

I'd conclude that noise is not just an issue of camera alone. But, I do agree that low noise camera is quite expensive. Currently, Nikon 3DS is crowned for the low noise king, regardless of amount megapixel issue. Visit www.dpreview.com for more details. The website also provides information how bad chroma noise level of each DSLR camera is.

So much for the camera stuffs, start shooting, it's more fun to do. Enjoy.