Step 1 - Open Your Canvas
Open up a new document 200x100, fill the background white. This will be the background for our first forum button.
Step 2 - New Layer
Create a new layer (Ctrl+shift+new), set the foreground color to black by pressing D on your keyboard.
Step 3 - Size Your Button
Select the rectangle tool and make a box the size you want the button to be. I want my button to be significantly smaller than the canvas I chose so mine looks something like this.
Step 4 - Add Some Style
Right click the layer you just made your button on and go to blending options, use the following settings for Drop Shadow, Inner Shadow, Bevel and Emboss and Gradient Overlay (Click Image To Full View).
Step 5 - Gradient
Create a new layer, select the gradient tool with the following settings. Create a gradient from the top of the rectangle to about halfway down as shown.
Step 6 - Opacity Settings
Move the layer 1px from the top of the rectangle by pressing the down arrow on your keyboard one time.. Lower the opacity to 20% in the layer panel as shown.
Step 7 - Another Gradient
Create a new layer and select the gradient tool with these settings. Create a gradient like in step 6 but this time go from the middle to the top.
Step 8 - Gradient Blend
To blend this gradient, set the layer mode to Overlay and lower the opacity to 15% in the layer panel as shown in this screenshot.
Step 9 - Add Your Text
Select the horizontal type tool (T) and type the text you want in white on the button. Set the text layer mode to Overlay and your done, here's how mine turned out:

