A good practice I use is to give users a "trial period" (usually 24 hours) before they must verify. Users can sign up for the site and immediately start using it, then next time they check their email just click the link. Many people will check their email at least once per day anyways.

Or, if they don't check it and try to log in after 24 hours, they get a message saying they need to verify their email address and the option to re-send the verification email.