Oauth helps, because people are more likely to have a decent password already for Gmail/Facebook/whatever than to make a new good password on the spot to try your site.

If you require an email address, you could send an email with a link (or code) to login and set a long loved cookie to keep users logged in. Again, it's likely that users will have a good password on their email.

Both of these options have negatives in that they tie your user to an external identity provider.