ASUS will release 3 new accessories for their Eee PC models. An optical drive, a hard drive & a 3G card.
The optical drive might come in handy if you want to install another OS onto your Eee PC, otherwise there's no real use for it. Why bother with taking 2 devices with you? The reason why people buy an Eee PC, is the fact that it is so small to carry with you.
The external hard drive looks a Western Digital Passport clone. Like the optical drive this doesn't look like a must have accessory, unless you use it at home. Sadly its not known yet what the capacity of the drive is.
The 3G card on the other hand is very useful, because it increases your mobility when there's no WiFi network in the neighborhood. The device is more compact then the current Huawei 3G USB modems.