Hi Mike...... there are several different ways..... depends on the picture (just what you wanted to hear, huh....)

..... you could use:
Channel Mixer with monochrome checked then adjust the sliders
or
Convert to LAB color and choose the Lightness Channel
or Desaturate..... or Grayscale ...... or Grayscale with a Duotone tint..... etc.....
How about posting a colored picture and letting us play around with it..... btw.... I love the photo....
Beth
ps.... you could also download (free) Virtual Photographer if you're wanting some different looks without having to spend a lot of time .....
http://www.optikvervelabs.com/