Kevin, 15 years into the 21st century, there is no real justification for anyone to keep any of us waiting 60 days to be paid. There are so many alternatives, such as PayPal, that we all use. I require nearly all of my clients to pay me a 50% deposit via credit card, then the balance when I submit the finished product. It is working well for me.
When I am working with a company who refers me to their accounting department to be paid, I always require the client to sign my short agreement in which I warn them I will charge a $50.00 late fee for every 2 weeks beyond the due date of my invoice. This is not perfect, but it works most of the time. When it fails, it fails big. A recent client who insisted on paying via paper check didn't bother to write the check for over 35 days. Then, after 3 more weeks, as the check never arrived, they had to go to their bank and pay $75.00 for a wire transfer because I politely but insistently bugged them about the bill.
My bank offers ACH deposit from any other bank - no charge. Most big banks offer this. The only thing to look out for is the "check" option - when your client thinks they are using on line ACH, and they don't select the proper payment option. Some banks then actually send out - grrrrrrr - a paper check via USPS mail.
I essentially modeled my system on Duane Russell's and it works 95% of the time. (Thanks, Duane!).