Comment An alternative (Score 5, Insightful) 572
Today Atmel, Microchip and others make inexpensive microcontrollers with native USB peripherals. The Atmel "8u2" chip, for example, is less expensive than even most of the FTDI clones, and certainly a LOT less than a genuine FTDI chip.
For years, I've published a very simple and easy-to-use USB code for those chips.
http://www.pjrc.com/teensy/usb...
I also publish a signed INF installer that works with ALL USB Serial based on this standard protocol (called Communications Device Class, Abstract Control Model, or CDC-ACM). All 3 operating systems have the necessary driver built in. Mac OS-X and Linux load it automatically. Windows needs the user to add a INF.
http://www.pjrc.com/teensy/ser...
Sadly, the CDC-ACM driver in Windows (called USBSER.SYS) is buggy. About a year ago, I sent Microsoft this reproducible bug report.
https://www.youtube.com/watch?...
In a follow up email a few months ago, they were supposedly testing a fix. I'm hopeful that Windows 10 may be the first version of Windows to ever ship with a good quality USB Serial driver (as Linux has done for many years, and Apple as done since releasing Lion a few years ago).