Here is a list of WordPress plugins that have conflicts with each other or with WordPress itself.
2
Better WP Security
Conflicts with social sharing plugins. It prevents fetching of meta data and G+ does not render properly. Use BulletProof Security or Login Security Solutions instead. (Tip from Jason Wiser)
1
Shareaholic
I use this plugin often, but at times it conflicts with my theme. I am now using Share This instead