RS232 Serial Port 34mm Express Card Adapter for Laptop

Pros: If you need to use a RS232 port for hardware control/development, this adapter may or may not suit that need (depending on that respective hardware compatibility). It's materials and finishing are more than decent at it's price.

Cons: As stated it the products' forum, it's just a Prolific USB-to-RS232 adapter, meaning it does not use the ExpressCard port's PCI pins, but it's USB ones. Thus, the only difference between this and a USB cable adapter is (beside the price) that you'll have one free USB port available. Other than that, it is very bulky, requiring you to reinsert it every time you pull your laptop out of the bag.

Other: If you need a USB port free while using an RS232 device with your laptop, this is the solution (besides, you know, an USB hub). If that is not an issue for you, save yourself some money and buy a cheaper USB-to-RS232 cable (you'll never know the difference).