Books

I've found reading books and attending training courses vital to my career development. In my spare time, I read books on communication, management and general personal skills. 

These are just a few of my recommendations...
Books:
Personal skills

• The Seven Habits of Highly Effective People Stephen Covey
• Understanding Misunderstandings Nancy Slessenger
• Get Anyone to do Anything David Lieberman 
• The 80/20 Principle Richard Koch
• Emotional Intelligence Daniel Goleman
• What got you here won't get you there John Maxwell
• Winning with People John Maxwell
• Talent is Never Enough John Maxwell 
• How to talk to anyone Leil Lowndes
• Super Confidence Gael Lindenfield
• Self Esteem Gael Lindenfield
• Assert Yourself Gael Lindenfield 
• The Ultimate Guide to NLP Richard Bandler
• Confidence and Success with CBT Avy Joseph and Maggie Chapman
• What's stopping you being more confident? Robert Kelsey
• Assertiveness Conrad & Suzanne Potts
• Resilience by Liggy Webb 
• Secrets of Resilient People by John Lees 
• Hard wiring Happiness by Rick Hanson
• Influence the Psychology of Persuasion by Robert Cialdini

Management and Leadership skills

• Managing for Dummies Bob Nelson and Peter Economy
• The Truth about Managing People Stephen Robbins
• Key Management Models Marcel Van Der Elst
• Leadership, Team Building and Culture Change Senn Delaney 
• Start with Why Simon Sinek

Writing Skills

• The Pyramid Principle Barbara Minto 

Marketing specific

• Email Marketing by Mullen Daniels
• Marketing Automation with Eloqua by Ben Griffith

PA specific

• The Definitive Personal Assistant & Secretarial Handbook Sue France

Videos

Management and Leadership skills

• How great leaders inspire action - http://www.ted.com/talks/simon_sinek_how_great_leaders_inspire_action.html