A few nice WordPress plugins I’ve been using recently:
Better WP Security – A very popular and powerful plugin that takes a range of steps to harden your WordPress installation.
Mail on Update – Emails you to let you know of available plugin updates.
Approval Workflow – An easy way to add an Administrator-approval process to your publications.
Blackbox Debug Bar – For plugin developers. It gives useful feedback on SQL queries, page load times, errors, and values of superglobals.