In the mail app, open a "new email" (the red "+" sign) and touch the "To:" box. You can add as many recipients as you want. There's a little "+" in the corner of the "to:" box that takes you right to your contacts.
If you hit the menu key, you will have additional options such as Add BCC, attach files, Add CC, etc.
I don't know if you can work this in the opposite direction (from the contacts list) for more than one contact at a time, but maybe someone knows the secret.