Webmaster Toolbox ~ Web Development Tools, Top Tips for Webmasters

Tips

Domain Name Registration: Registering with an ICANN Accredited Registrar, protecting your privacy, and marketing your website with the help of a well chosen domain name.
Search Engine Optimisation (SEO): The scientific approach to marketing a website.

Accessibility

Accessify Forum

Accessify Forum: Accessibility Discussion Forums

WebAIM Forums

WebAIM Accessibility Forums
Marketing

Digital Point Forums

Webmaster Forums - Internet Marketing & Search Engine Forums
Graphics
Lorelei Web Forum
Photoshop Tutorials, Webmasters discussion, Graphics, Web Development, SEO and Make Money Online

AVG Free 8.0 for Windows: General antivirus, anti-malware tool
CCleaner: User-friendly, comprehensive, temporary file deletion with secure (multi-pass) option
WinDirStat: Funky hard-disk filetype composition reports
FileZilla: FTP

Live, online lookup tools for instantly checking the facts and stats about websites, keywords...etc.

whois.domaintools.com: One of the most popular and universally-compatible whois lookup tools with links to further website analysis
ICANN Whois Report Generator: Most official tool - provided directly by ICANN, but doesn't support as many domain name extensions as some whois tools.
Nominet Whois Tool: Official whois lookup tool for ".UK" domain names, and only works for ".UK" queries.

Google Keyword Analysis Tool: By far the best keyword tool on the web, providing comprehensive access to Google's search data.
Google Trends: Google Trends for Searches historically summarises search volumes, with comparison between queries. Trends for Websites is Google's version of Alexa and Compete.
Google Insights for Search: Similar to Google Trends for Searches
Google Sets: Synonym generator
Search-based keyword tool: Another Google keyword tool