Webmaster Tools Online

Free Keyword

http://7search.com/scripts/searchterms/top_paying.asp?n=100
http://www.google.com/press/intl-zeitgeist.html
http://www.goodkeywords.com
http://www.nichebot.com

Analyse Keyword Density 

www.keyworddensity.com

Keyword Density Checker

http://www.searchengineworld.com/cgi-bin/kwda.cgi
http://www.pagerank.net/keyword-density-analyzer/

 Keyword Search Tool
http://inventory.overture.com/d/searchinventory/suggestion/

 Maxbid Tool
http://uv.bidtool.overture.com/d/USm/search/tools/bidtool/
 

AdSense Preview Tool
https://www.google.com/support/adsense/bin/answer.py?answer=10005&topic=160 

Google AdWords Keyword Tool
https://adwords.google.com/select/KeywordSandbox 
Scan your web pages to locate errors:

www.netmechanic.com/toolbox/html-code.htm 
Free Images from WikiMedia
http://commons.wikimedia.org/wiki/Main_Page 
Internet Traffic Monitor Report
http://www.internettrafficreport.com/main.htm
http://isc.sans.org/

To check anonymity

http://www.pcmesh.com/ip-check.cgi