Seasonality:
adlab.microsoft.com/ForecastV2/KeywordTrendsWeb.aspx
google.com/trends

Search Funnel (what is searched before and after a keyword)
adlab.microsoft.com/SearchFunnel/Default.aspx

Determining “importance” in google with cache dates:
webuildpages.com/cool-cache/

Site tech issues:
google.com/webmasters
siteexplorer.search.yahoo.com

Competitive analysis:
quantcast.com
spyfu.com
compete.com

Keyword analysis
tools.seobook.com/general/keyword/
quintura.com
seomoz.org/tools/kwtool.php

My favorite blogs:
seomoz.org
seobook.com
blog.outer-court.com

URL rewriting in Apache
webconfs.com/url-rewriting-tool.php