Search Engines, HTML Validation, & Link Checkers

Search Engines

Ask - Search engine owned by InterActive Corp. Promoted across their suite of properties. Google - the search engine with the largest reach.
Internet Archive - if you find any broken links you can see what those pages looked like in the past.
MSN Clustering Search - new technology search showing clustering.
MSN Search - the default search in Windows. Has around 10 to 15% market share in the US.
Yahoo! Mindset - search engine which allows you to bias your search results toward commercial or informational results.
Yahoo! Search - the search engine with the second largest reach.

How do Search Engines Work?

How Stuff Works: Search Engines - information about how internet search engines work.
Jeff Dean Video - leading Google engineer explains how search engines work.

What are People Searching for?

Yahoo! Search Term Suggestion Tool - gives 1 month data. For commercial queries numbers tend to run higher due to commercial forces that send automated search traffic.
Google Keyword Tool - gives 12 months of historical data
Dogpile Search Spy - shows real time search queries

Directories:

DMOZ - Open Directory Project
Yahoo! Directory - one of the oldest web directories
Yahoohooligans - web guide for kids
Wikipedia - similar to DMOZ in structure, but hosts articles instead of just categorized link lists

More Search Engines at:

Search Engine Watch