Discovery Store has the Planet Earth: Pole to Pole, Mountains & Deep Ocean DVD for only $1.99 (org $21.95) through 7/19 or while they last. Last I checked there were only 143 available. Shipping is $2.95. You can head over here to check it out.
If you sign up for their emails you can get a coupon for $5 a $25 order. You can check that out here.
Ebates: 5% cash back and $5.00 if you are new .
Shop At Home: 5% cash back and $5.00 if you are new.