I use a modified CP2102 based USB-TTL adapter cutting the trace of 3V3 (not needed, I use an AMS1117-3V3 in my handmade ESP-03 DevKit) and joining DTR to 3V3 pin for easy access. Here are the pictures of it:
You can buy it from my favourite EBay seller alice1101983.
http://www.ebay.com/itm/6Pin-USB-2-0-to ... 0565980256