I'm not sure if the "forever" keyword was ever involved, but two examples that spring to mind are Google Apps and Dyn, both of which have discontinued their free tier.
Not sure about Dyn, but if you had created a Google Apps prior to them removing the free tier - you still have it for free... new customers don't get to use it free but existing free customers are still free.
By the area codes provided by EvanMiller (415 = San Francisco, 650 = Palo Alto) I don't think he meant "free first, then they started charging". I think he meant "got acquired" / "pivoted" "went out of business".
Let's see. There was Apple's iTools, .mac, MobileMe, and now iCloud service (sort of one big evolving service, with some bits chopped off or replaced at various points in time), which has gone from free to paid to freemium.
There's Google Apps for your Domain, which killed off its free service in favor of the $5/user per month service.
Ning shut down their free service and switched to a paid only model.
DynDNS also shut down their free service, only offering paid.
I can't speak to the rest, but I still have free Google Apps for my personal domain. They're no longer offering it for new customers, but those who signed up when it was free still have it.
I recall those being free. I don't remember any of them being marketed as "Free forever". If you have even one example that you can document as being falsely advertised as "Free forever"...