Change font of selected text?

For various reasons, I find myself continually changing the font of text to Helvetica 12.0 point, and would like to be able to write a small script that I could assign to a Quicksilver trigger so that I simply need to select the offending text and hit a key combination to change the font. Anyone have any suggestions for how to go about doing this?

What application is the text in?

Well, that’s the thing. Sometimes it’s in Mail, sometimes in Text Edit, sometimes in something else entirely. Anyway to just do a “front application” sort of thing?