Just enter the code FREEMAIL305 at checkout.
The deal ends 5/1/10, so you only have about a week to take advantage of this. The fine print is below.
Disclaimer: Use coupon code FREEMAIL305 at checkout and receive $3.99 towards your final shipping cost. This amount is the US mail cost for a single book order. Please note: there will be a shipping total listed on your order receipt. This coupon code will reduce your final order total by $3.99, which is the US mail cost for a single book. Purchase must be 3rd party content. Self-purchases of your own content are not eligible. Discount cannot be used to pay for, nor shall be applied to applicable taxes or shipping and handling charges. Shipping destination must be a valid US address. Promotional codes cannot be applied to any previous order. No exchanges or substitutions allowed. Only one valid promotional code may be used per account. Coupon cannot be used in combination with other coupon codes. Offer expires on 5/1/10 at 11:59 PM. Lulu.com reserves the right to change or revoke this offer at anytime. Void where prohibited.