This video tutorial by portrait photographer Nathaniel Dodson (from the website tutvid) takes a look at at 3 ways of reducing noise in Photoshop.
Reducing noise is not a problem – you can easily remove all the noise from almost any image – the question really is how you can reduce noise but still maintain the details in your image which is what Dodson is trying in this video.
The first technique uses the smart sharpen tool to Reduce Noise (it has a reduce noise slider which you can use). This is nice but not the best technique in the world.
The second option is using the reduce noise filter – but not just simply using it (which is pretty bad) but by rasterizing the layer and duplicating the layer and using the noise filter. This still reduce the detail level of the image. What we can do is blend if slider to only effect certain colors which are more effected.
Finally, the best method is going to be camera RAW noise reduction. Go to the detail tab which has noise reduction – playing with the sliders here are going to be your best bet for a quick and easy noise reduction.