Lets start easy....
This is a nice tutorial to create a 3D sphere effect in Photoshop using standard tools.
The screenshots i used are quite low quality,
The result on your screen will be better (i hope haha)

First i started a new canvas 500*500 (easy to work with)
Of course you can make it as big as u want, but for a tutorial we will keep it smaller...
I painted the canvas in a greyish shade color for it will give the sphere more contrast

Now with the circular marquee tool, hold shift and make a circle selection (pic 1)

Then with the selection still active, click CTRL+C and CTRL+V
As you can see in pic 2 (below) we simply did a copy and paste, a new layer was added as you can see
Go to the new layer in the layers channel and right click the layer and go to BLENDING OPTIONS
Add DROP SHADOW/INNER SHADOW/SATIN and GRADIENT (pic 2)
I added my style settings also (pic 3 and 4)

Our sphere is taking shape as you can see....(pic 6)

And thats it really....
You can also play with the gradient tool to add other colors, play with the shadows (replace colors)

I took it even further and took another gradient color, duplicated the spehere layer again, scaled the layer and added bevel to the first layer. It gave me a nice 3D button shaped model. (pic 7 and 8)