I've been using this utility for about 20 minutes and I'm already a convert. Textpander allows you to make a shortcut for any string of plain/formatted text or pictures. In practice this means entering that regular url, email phrase or picture is just a keystroke away. It installs as a preference pane and a menubar item and allows you to get on with your business without typing out phrases for the ten millionth time in an email. Just pick a short word you would normally never use or a random keystroke.
Best of all it's donationware.
Address Book Groups in Mail
If you are sending out a group email and want to use a group you have made in Address Book, you can just drag over the group icon from Address Book into the Mail address field. An even easier way is to just type the Group Name in the address field. Mail will recognise it as a collection of email addresses. For instance I use a smart group called Dublin to collect all contacts with an address in the city. Simply typing "Dublin" into the address field will address the mail to all the contacts within that group. Tested under 10.4