Mail.app: How can Choose Signature choice be based on recipient?

I have heard on different podcasts of users who use TextExpander to shortcut into typing different e-mail signatures.

TextExpander is on my wish list of apps I will buy soon, I see a lot of potential in having keyboard shortcuts for common text snippets. Hope this helps.

If you turn on "Full Keyboard Access" for "All Controls" in System Preferences -> Keyboard -> Keyboard Shortcuts you can use Tab to navigate to the signature drop down. Or if you have already typed your message, Shift-Tab. Then use arrow keys to select the desired signature.

I've made my simple signature the default, and if I'd like to switch to the formal "external" signature, when finished with the email, I type shift-tab, and then the down arrow.