At the WordPress Sydney meetup a few months ago we had an evening (two even!) on security. Wil Brown gave an excellent presentation on general WordPress best practices, as well as useful security plugins, and even more practices for the extra paranoid. Check out the WordPress security presentation on Slideshare.
Since then Wil has also released an infographic on WordPress security best practices.
I spent a good part of the last week cleaning up a WordPress hack (not my fault!), which prompted me to revisit this information, and inspired me to spread it to as many people as possible. Seriously, check out the infographic and presentation: they are gold!