I recommend Conversion Rates Experts (<a href="http://www.conversion-rates-experts.com" rel="nofollow">http://www.conversion-rates-experts.com</a>). Mainly, the CrazyEgg case study (<a href="http://www.conversion-rate-experts.com/crazy-egg-case-study/" rel="nofollow">http://www.conversion-rate-experts.com/crazy-egg-case-study/</a>) -- love how they approach collecting qualitative data.<p>Also, the guys at Unbounce does a great job with landing pages A/B Testing (<a href="http://unbounce.com/blog/" rel="nofollow">http://unbounce.com/blog/</a>).<p>Patrick, a fellow HNer (<a href="http://news.ycombinator.com/user?id=patio11" rel="nofollow">http://news.ycombinator.com/user?id=patio11</a>) writes a blog on marketing for software (<a href="http://www.kalzumeus.com/blog/" rel="nofollow">http://www.kalzumeus.com/blog/</a>) and other tips for developers.
Not books, but I always read these blogs:<p><a href="http://visualwebsiteoptimizer.com/split-testing-blog/" rel="nofollow">http://visualwebsiteoptimizer.com/split-testing-blog/</a><p><a href="http://blog.optimizely.com/" rel="nofollow">http://blog.optimizely.com/</a>
Google described their process here:<p><a href="http://static.googleusercontent.com/external_content/untrusted_dlcp/research.google.com/en//pubs/archive/36500.pdf" rel="nofollow">http://static.googleusercontent.com/external_content/untrust...</a>