 This is a good tutorial to begin with in Illustrator for using Illustrator's built-in effects to create textures. In this case, we'll be creating a "grungy" metal look.
1. Type out some text. The Font you choose and its' size should be bold and big enough for the texture to appear inside of. I used Myriad Pro, Bold, 72 pt.
2. We now need to convert the text into paths (or outlines) so a gradient can be applied to it. So, Right-click on the text and choose "Create Outlines".

3. Now click on the White, Black gradient in the Fill panel. (See below.)

4. Now we're ready to begin adding the effects that will produce the metal text.
#1 Effects > Brush Strokes > Accented Edges

#2 Effects > Texture > Craquelure

#3 Effects > Artistic > Film Grain

#4 Effects > Artistic > Dry Brush

Now all that's left is to add a Drop Shadow:

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