Gather all of your flagged messages into one area - a Smart Mailbox... and have it update automatically as you continue to Add/Remove flags from them.
Open Mail, Then from the menu, choose MAIL->New Smart Mailbox.
Next, type in a name for the new mailbox, I am using 'Follow Up' Also, set the criteria - 'Contains messages which match 'ALL' of the following conditions'.
Now, from the drop down menu, select 'MESSAGE IS FLAGGED'. Optional: Include messages from Sent or Trash Click 'OK' Now, you will have a new folder appear with your flagged messages. Click on it, and you will be presented with any messages you have 'Flagged' from now on.