The new HD cameras have forced pixel density to new highs and as such the low light ability of the newer cameras are not performing as well as their older SD predecessors. With modern digital signal processing, some noise can be reduced.
This tip is for those who cannot and/or will not use lights but shoot in low light scenarios. Basically if you don't like using gain, limit it to -6 or even 0db(this measurement varies from camera to camera). For those with cameras that cannot limit gain, use manual aperture control and keep it above where you start to see any noise. * It is also very important to keep shutter speed at a minimum of 1/60 in 60i. 1/50 in 50i, 1/60 in 30P and 1/48 in 24P to prevent the strobe look. For those cameras with 24P recording, use that mode to get 1/48 to maximize light. However, with 24P, your camera control has to be slow as quick panning can cause strobic effects. Furthermore, with faster moving subjects, 1/48-1/60 may not be quick enough to prevent subject motion blurring. This is important for those who want to do slow motion in post.
It doesn't matter if the picture looks a bit dark because as long as it remains clean and free of noise, you can bring it up by up to 2 stops in post, often without too much detrimental effect on the noise and grain.
It is also a good thing to use a color filter to maintain color and compensate for gamma and gain in post. A filter kills about 1.5 to 2 stops.
Post production boosting can be done by most NLEs. By using post instead of pushing the camera, one can maintain good shutter speed and noise characteristics rather than use gain and ruin detail and color.
Stronger color correction facilitated by some NLE like Final Cut Studio's Color or Red Giant's Colorista (which works with Adobe CS3 After Effects, FCP and Motion.
Samples may follow 
