Sorry, but that's not a typeface you're describing, but rather an encoding. Pretty nearly all fonts these days use Unicode. UTF-8 is a specific way of representing Unicode text.... "Unicode 6.0 UTF-8" is kind of like saying ASCII or MacRoman or Win-ANSI. It describes a character set and encoding, not the name of a typeface or a font.
I think that TextWrangler used to use Monaco as the default font. I think they may have changed to Consolas (the big sibling product, BBEdit, uses Consolas, hence my theory). I would check my installation, but of course the first thing I do is mess with the default font settings....
On the Mac, Dreamweaver CS 5.5 defaults to Times New Roman in preview, and Monaco in code view.
So I think what you may be looking for is Monaco, which is a Mac system font. It isn't available on Windows, however. The closest alternative that is more broadly available would be Mark Simonson's Anonymous Pro, which is modeled in large part on Monaco. Or you might even want the older version, Anonymous, which has an "a" more similar to Monaco.
These are both available at no charge from the designer (despite the URL):