What would be a good way to send sensitive information to users that are not very tech-savvy?

As web developers we need to supply sensitive data to the clients. Clients are usually not very good with computers. They can send an email, pick up a phone call or open a webpage. But won't be able to set up PGP in their email client.

What would be a good way to send them their login credentials? Are there any services that can help us with this? It needs to be reasonably simple and reasonably secure (generally more secure then sending in an email).

Problem with most ready-made solutions (Basecamp, Slack) is that they send you an email notification with message contents.