Use a two-factor auth plugin like https://wordpress.org/extend/plugins/google-authenticator/ It works with the Google Authenticator app. Duo Security is also good: http://wordpress.org/extend/plugins/duo-wordpress/ The WordPress.com team have already announced two-factor auth support for wp.com blogs, and are working on an official solution for wp.org sites: http://macmanx.com/2013/04/12/two-step-authentication-on-wo…
For 2/3 of the WordPress sites I administer, I use a very long, complex admin password. The other site is for a group that wanted multiple admin accounts, but the people who use these accounts have a lot of trouble with complex passwords. After several emails telling me that "the website doesn't work" because the user had trouble with a long password with special characters, I gave up and switched it to an easy-to-remember password with just uppercase and lowercase letters.