I used CIBT, our company's agency. I did hubby's crew visa with them. They have a separate account for family members and offer a discounted rate for services. I couldn't stomach their $34 fee for next day UPS label each way, though, so I bought my own for much less.
My invitation letter required a photo ID of the host, along with address in China, phone and other info. My friend got out her passport and discovered her visa was about to expire--she usually gets a one year and somehow the current one was issued for 90 days. Good thing I asked her to do the letter; she would have overstayed her visa! So, my letter was written by her Spanish husband (he's a corp pilot in China) and he sent his ID.
I love your last comment about the Chinese, yeechoong! What a hoot!