In Outlook 2010, can you add "Categories" to the "New Email" Ribbon?

I couldn't figure out how to do this in Outlook 2007, and I was hoping I could do it in Outlook 2010... I want the ability to quickly apply a category when composing a new email (typically a "Waiting For..." category) for things that need a response.

It is possible to apply a category by clicking the "Options" ribbon, then the little arrow under the More Options section - but why can't I get the nice big "Categories" drop-down that's available in the "Tags" section of the main Outlook window. There are about a kabillion commands in the "Customize Ribbon" dialog box for the New Mail window, but I couldn't find anything about Categories. Should I just give up?

You need to open the "Visual Basic Window" (Alt + F11)

Add a Module (Right-click "Modules" Folder > Insert > Module) and copy & paste the below:

Public Sub CategoriesButton()
  Dim Item As Outlook.MailItem
  Set Item = Application.ActiveInspector.CurrentItem
  Item.ShowCategoriesDialog
End Sub

For Outlook 2010

1. Click the "New E-Mail" Button

2. Right Click > Customize Ribbon > Drop Down > Macros > Select "Project1.CategoriesButton" and add to a new group.

3. Rename and Add icons to the button as you wish!

I have a solution that I prefer to the others listed -- it's very similar to William Jackson's, with one very important difference.

I have a rule that takes action after I send a message, but instead of looking for visible text, as in William's solution, it looks for an uncommon whitespace character. I simply don't want the recipient to see text in my e-mail that isn't intended for them.

For my whitespace character, I chose the "En Quad" (U+2000) for two reasons: it's easy to remember (2000) and it's hardly ever used. My rule simply looks for the en quad in the body of the e-mail upon sending. So for those e-mails that I want to apply my category of "Waiting for Response", I simply press 2000 Alt-X. The Alt-X replaces the numbers with their corresponding Unicode character. With a few quick keystrokes, I've marked my e-mail with my custom category.

You can create a Rule that will automatically categorize a message after you send it based on specific words in the body. If you can swallow putting a keyword in the body of the email, this should be an easy way to do it.

For example, I created a Rule that applies after I send a message with "cat:waiting" in the body, assigning it to the "waiting" category. Then at the end of an email I just type "cat:waiting" and Outlook will categorize it according to my Rule when I send it.