Step 1 - The inevitable "New Document"
Open Photoshop and create a New Document.
For the purpose of this tutorial, we have a document 630 pixels wide by 300 pixels high but as your button will likely be cut away from this eventually, just give yourself enough space to work.
Step 2 - Button base
The metallic RSS button is going to be round, so using the Ellipse Tool (U) with a medium to dark grey - I've gone with #454545 - draw your circle.
Next go to the Layer Styles (double clicking the layer) and check Gradient, applying the following settings.
Finally, merge this with a blank layer so that we have a flattened image.
Step 3 - RSS Icon
Create a new layer and select the Custom Shape Tool (U), with the custom shape "Bull's Eye". Using a Chroma Keyer colour and draw a Bull's Eye over your button base, 5 - 10 pixels past the edge.
Now use the Rectangular Marquee Tool (M) to select and cut away the left side and lower half of the Bull's Eye, also removing the remaining quarter of the centre circle.
Use the elliptical Marquee Tool (M) to draw in your own full circle, aligned to the left and lower area of the outer rings then drop it down into place, aligning it with the button base.
Step 4 - Metal die cut
Duplicate the button base layer, Ctrl + Click the RSS icon layer and press delete.
You can now remove the RSS Icon layer and make the base button layer hidden to see what you've created. You should have a RSS Button that looks like this:-
Step 5 - Metal texture
To create the metal texture, apply the following Layer Styles to the metal die cut:-
Apply a Clipping Mask to the two layers (Layer > Create Clipping Mask) and you should now have a Metal RSS Button looking a little like this:-
Step 6 - Brushed metal
Again duplicate the button base layer and bring it above everything.
Apply a Noise Filter of around 125%, Gaussian and Monochromatic (Filter > Noise > Add Noise).
Ctrl + Click the layer so we have a selection and apply a Radial Spin (Filter > Blur > Radial Blur > Spin / 100 / Good.)
Set the layers Blending Mode to Multply and bring the opacity down to around 15%.
Step 7 - Some shine
Finally, add a little shine by duplicating the button base layer, raising the lightness to 100% so that it is a solid white and place it above everything. Use the Elliptical Marquee Tool (U) to select around a two thirds area and press delete.
Set the Layer Blending Mode to Overlay and drop the opacity down to around 60%.
Add a vector mask and using a soft edge brush of around 25%, gentle brush the top edge away to give a more gentle shine.