SEO & SEM Tools I Like

15 Minute SEO

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

Compete.com:
Compare unique visitors to multiple domains; trend over time.

Covario Podcasts:
SEM oriented podcasts

Dig PageRank:
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.

Google Adwords:
PPC program where webmasters can create their own ads and choose keywords.

Google Inside Adwords Blog

Google Adwords Certification

Google Conversion University

Google Labs

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.

Google Tools:
Blog post discussing 57 Google tools outside the scope of many of the SEO/SEM ones shown here.

Google Trends

Google Webmaster Central

Guidelines on ALT texts in IMG elements

How keyword length and ad position impact CTR and CPC on Google AdWords

Insight24 Presentations

Max Characters in a Title?

MSN Keyword Forecast Tool

Quantcast Traffic Comparison Tool:

Seebot.org:
See the web like a crawler.

SEO Copywriting:
Description of the search engine optimization technique of SEO Copywriting, including details of its strengths and weaknesses.

WebPage Analyzer:
Website performance tool and webpage speed analysis.

WebTrends Resources

WordTracker:
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