rfgoetz on "[Plugin: WP-TopBar] Add subscribe (mailchimp) form to topbar?"

Reading the MailChimp List Subscribe Form plugin (http://wordpress.org/extend/plugins/mailchimp/installation/), you should be able to generate the form by putting this code in the new PREFIX PHP section:

mailchimpSF_signup_form();

You might need to add breaks: e.g. echo "</br>";