Great post topic! I spent ages trying different plugins, some work, some dont!

At the moment all of these are working well without slowing the site down too much:

GRAND flash album gallery – flash photo gallery
ShareThis – facebook, twitter, email etc share buttons
Simple image link – I've used this as a widget in left sidebar to link to facebook and twiiter via a logo
Tweet Old Post – Plugin for tweeting your old blog posts randomly
Twitter Badge – Twitter badge link appears to float on rhs
Wordbooker – Automatically posts to facbook page when making a new post
Wordpress.com Popular posts – Used as a widget to show most popular posts in sidebar
Wordpress.com Stats – Tracks post/page views referrers and clicks
Wordpress Tweeter – Automatically tweets every new blog post
WP Super cache – 'Very fast caching plugin'

I have recently had a problem with Web Ninja Google Analytics slowing the whole site/dashboard down when activated. A very good plugin for web analytics but my site jkust didnt get on with it!

I hope this helps other people, it can be a timely exercise trying different plugins!