It's been a while since I've used photoshop. But generally speaking, if I need to find the RGB value of a pixel in any graphics package (usually gimp/paint.net/inkscape), I'd zoom right in on the image so I can see the pixel I'm after and use the colour picker tool (looks like a pippette / eye-dropper) to select the pixel.
This action will usually set your active colour (either the foreground or background colour) to the same colour as the pixel you clicked on with the colour picker. Next click on the colour (the one that changed when you used the colour picker) and you'll usually get a popup which shows more detailed info on the properties of the selected colour. (HSV, RGB, and HEX values).
Trust me it sounds much more long winded than it actually is...It only takes a second or two to do, so it is a pretty quick method!
Like I said, I haven't used photoshop in a long while, but the method I've described can be used in most decent photo editing software nowadays and I'd assume that photoshop will be no different!
Alternatively, there are loads of little tools that are freely available that will allow you to view the colours of pixels anywhere on your screen. If you're on windows, there is a little .NET based tool I've been using on my windows PC's called cpix.exe (google it and download it!).
This neat little tool opens a small window which stays above all other windows. Inside the window you'll see RGB details of the pixel currently under the mouse cursor. There's also a magnifier which shows the area around your mouse cursor. You can use it to zoom in on images and examine the colours of individual pixels. Pressing the spacebar will lock cpix to the pixel your mouse is hovering over. You can then make a note of the RGB value and use it in your photo editing software/html page/whatever!
I'm sure there are similar tools available for other platforms!
Anyways, hope this is of some help.
Cheers for now,