I've been developing websites on Wordpress for a couple of years at this point and every time I start a new website I have to go searching for all the plugins that I frequently use. I wanted to create a list of the essential Plugins that I often install:
Broken Link Checker:
It's not good to have broken links on your site, and so even if its a minor outage, Broken Link checker can notify you.
Really cool plugin that takes whatever the users typed into the url and searches your site for any matching content.
Yet Another Related Posts Plugin:
A great post to group related posts together at the bottom of each article. I always use a site cache so the speed impact is minimal with a plugin like this.
Disqus Comment System:
I really haven't got anything against the built in Wordpress comment system, but I noticed I myself was more likely to join the debate on other sites when they used Disqus, well there's a testimonial I couldn't ignore! I've since put it into all my main sites to offer threaded replies, email subscription and RSS options and built in Akismet spam protection!
WPtouch iPhone Theme:
Great instant iPhoneable theme for your site. It instantly serves a different site when someone on a mobile browsers brings up your site, and it also lets you go back to the default if you want to squint!
I have begun using only three share options, Facebook like, Twitter re-tweet and Google +1. I use the default buttons after my content, idea being I want people to share content they've enjoyed not spam my content to their friends before they even read it . . .
I haven't really investigated my cache options but this one works for me. a tip from my troubles: always hit the clear cache button if you change anything in your theme widgets, I had the hardest time figuring this one out one afternoon!
Hopefully this saves some time, I know I'll be referring to this list next time I start a new website.