Backlink Builder - Submit your website to huge bunch of web directories.
Google Adwords: Keyword Tool - Check popular keywords and get suggestions on alternative keywords.
Google Insights for Search - Check keywords searches based on location and other variables.
Website Value Calc - Get a rough idea on your websites value based on popularity.
KeywordSpy - Check your competitors PPC keywords.
Google Search Based Keyword Tool - Check keywords search volumes, based on real searches.
Google Trends - See what people are searching for, now and in the past.
WordTracker - A good alternative to Google's keyword tool.
NicheBot - Another good keyword tool.