SEO & SEM Tools I Like
A|B Split Optimizer
Abakus Keyword Analyzer
Character Counter& Word Count Tool
Calculate the number of characters in words in a selection of text.
Check Server Headers Tool - HTTP Status Codes Checker
Code Similarity Checker
Commas in Keywords
Compare unique visitors to multiple domains; trend over time.
SEM oriented podcasts
Check your pagerank rank with digpagerank in over 700 datacenters.
Drupal and Robots.txt
GLYNC Add-on for Firefox:
Glync is a Firefox extension which adds historical graphs to the External Links page in Google Webmaster Tools.
PPC program where webmasters can create their own ads and choose keywords.
Google Inside Adwords Blog
Google Adwords Certification
Google Conversion University
Google, Matt Cutts' Blog
Google Page Rank Explained
Google Rankings Keyword Density Analyzer:
Enter the domain or URL of your website to see which are the words
and phrases it uses most, see a detailed report on their numbers and density.
Blog post discussing 57 Google tools outside the scope of many of the SEO/SEM ones shown here.
Google Webmaster Central
Guidelines on ALT texts in IMG elements
How keyword length and ad position impact CTR and CPC on Google AdWords
Max Characters in a Title?
MSN Keyword Forecast Tool
Quantcast Traffic Comparison Tool:
See the web like a crawler.
Description of the search engine optimization technique of SEO Copywriting, including details of its strengths and weaknesses.
Website performance tool and webpage speed analysis.
Free keyword suggestion tool.
WorkTracker Labs Keyword Question Tool
Writing Effective ALT Text for Images
Yahoo!, Optimizing For
Yahoo! Search Marketing Blog
YouTube B2B Event 6-6-8