General Webmaster tools:

Web Page Analysis
Web Page Analyser - http://www.websiteoptimization.com/
This tool is useful for checking how long your webpage takes to download on various connection speeds and offers advice on how you can tweak it. A lot of potential visitors can be put off by long loading times so it is vital to make sure that your page loads quickly and efficiently.

HTTP / DNS Information
Rex Swain's HTTP Viewer - http://www.rexswain.com/httpview.html
This tool is useful for getting some of the background information about the page - seeing what a search spider sees whilst crawling your page (including error codes, server-side redirects and meta-refreshes). These tools can help to identify redirection problems with your site.


Software and Plugins:
Firefox - http://www.mozilla.com/en-US/firefox/
Firefox is our browser of choice mainly because there are a number of ways that you can extend the functions of the browser (IE7 is also available as a comparison). Extensions for Firefox include Adblock (to block adverts and popups), the Google toolbar and Greasemonkey (which allows scripts to modify the layout of pages - one of the most useful scripts numbers the results in Google).