Sometimes, whether in testing or other situations, you need to reset a password (often the admin password) for a Drupal site.
Edit: The shortest answer is that two wonderful options are built into drush!
# Get an admin login link
# Set the password for any user
drush upwd admin --password="newpassword"
(More info on drush uli below.)
Now for the long version
In Drupal 6, you could just reset the admin password with:
drush sql-cli # or mysql -u<user> -p<pass> <drupal_db>
UPDATE users SET name='admin', pass=md5('drupal') WHERE uid=1;
and then log in with username 'admin' and password 'drupal'.
But no more. Drupal 7 has a unique hash for each site, which means you can't just use the md5() trick any more. However, there is a script in the scripts directory that will do this.