(Update) MAY 2014 ~ Essential WP Plugins for WordPress 3.9

This is a short-list of plugins for WP 3.9 which I am considering to use.
Please indicate which you prefer and if you have any other additions or must haves, please include in your post.
Which have you found to be resource hogs?
Have you had any experience of conflicting plugins?
etc...etc....

Please discuss and outline which you have found to be the best. Thanks for your help.


SEO

WordPress SEO by Yoast

SEO Ultimate

All in One SEO Pack

Google XML Sitemaps

SEO Smart Links


Cache

WP Super Cache

W3 Total Cache

Quick Cache

WP Fastest Cache



Backup

BackWPup


Contact Forms

Contact Form 7
Visual Form Builder

Search

WP Ultimate Search
Better Search

Security

iThemes Security / Better WP Security
Better WP Security

Limit Login Attempts

Sucuri Security

Wordfence Security



Spam

Akismet
Antispam BeeBad Behavior
AVH First Defense Against Spam
Spam Master

Statistics

Google Analytics for WordPress
WP SlimStat
FeedStats
WP-Stats-Dashboard
Word Stats
Simple Feed Stats

Social Media

Social Login
ShareThis
Shareaholic
Social Metrics
Social Networks Auto-Poster

Email Marketing

Benchmark Email Lite
WordPress PopUp
SendPress
MailPoet Newsletters

Mobile

WPtouch
WP Mobile Detector Mobile Plugin
WiziApp
Visual Editor


Community BuddyPress
bbPress
Images
NextGEN Gallery

Management

Yet Another Related Posts Plugin (YARPP)

Ultimate TinyMCE

TinyMCE Advanced

Duplicate Post

Post Type Switcher

WP-Optimize

Broken Link Checker

ManageWP

Jetpack

Theme-Check

WP Auto Affiliate Links

WP Content Copy Protection

S2member is a very good membership platform you may want to consider using and it is free for the basic version.

Note that more plugins mean more vulnerability. Some of these plugins can be coded with php coding if you're willing to learn for a few hours. It really goes far once you understand how to do it.