Buy.com this week is offering the Cables Unlimited BatteryBoost for iPhone 3G and 3GS (model no. BAT-9000) for 57% less than its $69.99 list price, which places this device at only $29.99 and makes it the best cost we could find for this external battery anywhere else. FREE shipping is included and sales tax applies for residents of New York and California.

For the times when you’re at home Buy.com also has the iPhone 3G and iPod touch Docking Station with remote, which is designed to connect the mobile device to the user’s home theater system and can be purchased for only $14.99 with FREE shipping included. Amazon.com is also offering a docking station today, the Kensington Charging Dock with Mini Battery Pack for the iPhone and iPod. This Kensington dock can extend the iPhone’s video playback by up to six hours and is currently on sale for $45.49. A more portable solution is the Macally Powerlink 30-Pin Portable Battery Charger for iPhone/iPod, which unlike the featured product is more designed to attach to the bottom of the iPhone instead of wrapping around its back and sides. The Macally sports a sale price $30.57 and is said to offer up to 3.5 hours of additional talk time or 1.5 hours of video playback.

The Cables Unlimited BatteryBoost for iPhone 3G and 3GS combines the benefits of an external battery with a thick hard casing that protects the back and sides of the iPhone. While attached to the iPhone the case is said to almost double the battery life of your iPhone, and allows users to charge both the iPhone and the case simultaneously. Dimensions: 0.3” x 0.3” x 0.3”; weight 10.7oz.