hi
i recommend these:
wp-likes
a simple plugin to like posts and if you choose from it's settings, people can like pages
also works with wp super cash
autoptimize
this plugin optimize's your wordpress site and minifie's CSS and javascripts pages, so your website load's faster
all in one seo pack
as it's name says, this plugin is for optimizing seo
it has many options, but some of them for advanced users
broken link checker
if your external links break, this plugin notify's you