A useful list of social media tools from get2growth.com/ (see the resources section for more useful stuff).

Social / Influencer Tracking

PeerIndex – Measures social interactions across the web to help you understand the people you influence online (Twitter, LinkedIn, Facebook, Quora)
Little Bird – On demand expert and influencer discovery and engagement tool validated by their peers on any topical community (Twitter, LinkedIn, Facebook, YouTube, Google+)
Traackr – Tool for finding the right influencers through social media and understanding how to engage with them.
Mentionmapp – Twitter network analysis and data visualization.
Topsy – Measurement and analysis tool for social conversations to identify key thoughts, opinion and content being shared over time or in real-time (Twitter, Google+)
Klout – Social media analytics tool that scores and ranks users’ influence using a ‘Klout Score’ from 1 to 100 ( Twitter, Facebook, Google+, LinkedIn, Foursquare, Wikipedia, Instagram)
CircleCount – Google+ profile statistics and influencer measurement.
Kred – Uses social data and influence measurement to produce a personal visual stream from Twitter ID activity or hashtags based on communities connected by interests and affiliations.
twtrland.com – Visualizes social footprints to help you discover new connections, understand their impact and find better ways to connect.
Followerwonk – Twitter analytics, follower segmentation, social graph tracking, and more.
who.unfollowed.me – Check your Twitter unfollowers, see who is not following you back and who you are not following back.
Radian6 (Salesforce Marketing Cloud) – Social media monitoring tools, social media engagement software and social marketing.

Social Media / Content Management & Marketing
Buffer – Tool for collating and sharing online content via social feeds throughout the day.
Hootsuite – Social Media dashboard to manage and measure across social networks.
Tweetdeck – Twitter management and insights dashboard for power users.
Ning – Online platform to create custom social networks from scratch or to integrate with current sites; also integrates with Facebook, Twitter, Google and Yahoo!
AddThis – Social infrastructure and analytics platform with personal and social web sharing tools.
DivvyHQ – Content editorial planning and production tool.
Kapost – Software platform for organizing content marketing into a structured business process with calendar, workflow and analytics.
Compendium – Orchestrates all of the content necessary to maintain a consistent message for your brand from both inside and outside your company.
WordPress Editorial Calendar – WordPress plug-in allows you to set up all your posts in a simple calendar format with clean interface that allows you to drag and drop blog posts to better manage your ideas.
Publicate – Easily organise your content or content you’ve discovered to share, publish and showcase.

SEO / SEM & Keyword Research
Google Keywords – Enter keywords or phrases to see what related word searches your ad will show on.
Wordtracker – Keyword research tool to discover high performing keywords based on your subjects and messages.
SEMrush – Keyword and competitor research tool providing ad copies and positions, organic positions for domains and landing URLs, search volumes, CPC, competition, number of results, and more.
WooRank – Website review and SEO tool for tracking and optimizing your site.