Lots of different techniques out there and as usual it very much depends on your image as to which one will work best.
As mentioned you can use a seperate plugin to give you numerous options or if you prefer you can have a go and use the tools with in photoshop.
I have recently been using a technique called contrast grading
http://www.ianbarberphotography.co.uk/convert-to-black-and-white/ which I am finding very useful as it gives you total control over the all the elements that make up your image.
Another good one is Guy Gowan's colour to mono.
http://www.guygowan.com/shop/dvd/mono/
I have just tried thie technique below today and so far I think the results are good defenatley one to remember for the future.
The Gorman-Holbert Method
This black and white conversion method is named for Greg Gorman and Mac Holbert.
It is a luminosity based method especially good for portraits and delicate subjects
1. Convert to LAB colour (image/mode)
2. Select Lightness channel (in the channel palette)
3. Set Image mode to Greyscale (image/mode) when asked discard other channels
4. While holding the CTRL key click on the Grey channel to Select Shadows
5. Invert selection (select/invert)
6. Convert image back to RGB (image/mode)
7. Go to the layers palette
8. Create new fill layer and fill with colour or grey whatever you like (sepia R225:G141:B31 is a good place to start) (Grey R150:G150:B150) you can always change the colour later if required)
9. Change blending mode of the fill layer to multiply
10. Create new merged layer above this by clicking on the fill layer then pressing CTRL,ALT,SHIFT, E
11. Change the blending mode of this new layer to Overlay and adjust the opacity to 20%
12. Run High Pass sharpen on this layer set at 50 pixels (filter/other/high pass)