There are lots of posts dedicated to showing you wordpress plugins that enhance your post functionality and add features but not many that focus on helping you clean and maintain a secure and orderly backend.
OK maybe that was a bit overly dramatic but really these two EVERYONE should be using:
Wordpress Automatic Upgrade - This one absolutely makes upgrading a breeze. I can't tell you how many man hours this one has saved me.
Wordpress Database Backup - really nothing sucks more than losing a blog because of a catastrophe and this gives you the ability to send a daily backup to an offsite storage location via email (say something like a dedicated gmail account for instance)
Ok now onto the stuff you may not have seen already...
• Broken Link Checker - link rot it happens, chances are if you link out a lot or have been blogging for more than a year your blog has some dead links. This plugin will run thru them all identify them and let you fix,update, delete, or unlink them... yea I know cool huh. Warning the first time this thing runs it's pretty labor intensive, so choose a less busy time like a holiday weekend to first turn it on.
• Cross Linker - So lets say you've written a great review post of that snazzy new Blackberry Curve you just bought. Your post is so great every time you write the words "blackberry curve" you want it to link to your review post, but you know... you're lazy or forgetful. Cross linker will do the deed for you. it won't overwrite where a link already exists, and you can also set it only link the first occurrence of the word so your posts don't end up looking like intellitext on steroids or something.
• Go Codes - Maybe your an affilaite and you'd like redirect all of your affiliate links through a script for tracking purposes or maintenance purposes. use GoCodes to set up a tinyurl like function on your blog so http://example.com/go/blackberry-curve/
sends people to your aff link. Want to change affilaites... easy peezy just update your go code instead of every link... neat huh. if you combine this with Cross linker above it becomes really powerful. You can set up cross linker to link to a gocode page... did we get a lightbulb moment...
• Login Lockdown - Hacking wordpress is really becoming an issue lately, and anything you can do to slow people down is a good thing. login lockdown will block IP's after a specified number of incorrect username/password combinations. You can configure some of the options, not perfect nor fool proof but it's a start.
• Audit Trail - Keep track of who did what and when they did it. Especially helpful when you have multiple admins, editors, or authors around.
• Wp Security Scan - Sounds much more impressive than it actually is, but still it does some useful things and makes some good suggestions. Looks like the author also has some good ideas in the pipeline so it's one to keep an eye on.