User Research

• Interviewing and Observing Users - D-School Stanford
• [webinar] Marketing, Meet UX - (good overview of using research for improvents) - KissMetrics
  
• Step-by-Step Guide to User Testing - UX Sisters
  
• Reframing and Brainstorming Process - D-School Stanford

Qualitative:

• The Advanced Guide to Qualitative Research - Conversion XL
• Using Live Chat (on your website/product) for Research - HubSpot
• [case study]: How Poll Questions Can Be Optimized to get Better Responses - Hotjar
  
• How to Conduct Market Research on a Tight Budget - HubSpot
• How to Get Survey Answers that Actually Help your Business - KissMetrics
  
• Guerrilla Research Tactics and Tools - UX Booth

Quantitative:

• Setting Up and Auditing Your Funnel - KissMetrics- (written for a SaaS, but apply same idea to websites) 
  
• What Marketers Need to Know About Cohort Analysis - KissMetrics
  
• Advanced Google Analytics (filters, segments, reports) + Funnel Video - KissMetrics

Observational:

• Hotjar Observational Action Plan - Hotjar
• 7 Heatmap Case Studies - CrazyEgg
• [case study] Using Heatmaps to Identify Friction & Solve - Hotjar

Usability

• [ebook] A Complete Guide to User Testing Your Next Project - UserTesting.com

• 8 Tips for doing Usability Testing Quickly - HubSpot
  
  

conversion rate optimization (cRO) & SPlit testing

• [video] A/B Testing Done Right - Google Ventures Lab w/ Optimizely
• Optimizely Academy - Optimizely
• Where should I start testing + How to prove value over time - Optimizely
• A/B Split Test Duration Calculator - VWO

Beginner Guides to CRO:

• Qualaroo's Guide
  
• QuickSprout's Guide
• Holy Grail of CRO - Steps to Follow - YouMoz Blog
• 666 Tips & Resources for CRO/Testing Ideas - Oli at Unbounce

Example Tests / Case Studies:

• WhichTestWon.com
• 100 CRO Case Studies - Optimizely

More coming soon...please check back!