5GL use and recommend the following resources -

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Domain Names
easily.co.uk
Check availability and register domain names. Excellent prices and service.

Search Engine Optimisation
selfpromotion.com
A superb site full of articles on how to prepare your site for search engine submission, create keywords, pitfalls to avoid, etc, plus an excellent search engine submission tool.
Overture Search Term Suggestion Tool
Enter a very general keyphrase (like "real estate") and it tells you all of the more specific keyphrases that relate to that keyphrase and how many hits they got.
Search Engine Primer
A free downloadable eBook to help you optimise your site for search engines.
Successful Site in 12 Months with Google Alone
Excellent article on how to modify your site to get a high ranking on Google (and other search engines)

Internet Marketing
Internet Marketing Center
The Insider Secrets to Marketing Your Business on the Internet is the #1 best-selling internet marketing course online. It has been termed as by far, the best online promotion and marketing information available.
sitesell.com
Since 1997, SiteSell.com books and software have empowered over 100,000 entrepreneurs and small businesses to outperform larger, well-financed competitors. They will do the same for you.
Website Traffic System

A excellent collection of eBooks, software and tips to drive traffic to your site.

Traffic Builders
Trafficswarm.com
A free traffic generation system that displays links to your site when visitors exit other members sites. A good way to increase hits.

Software
Mailloop
The best software around to automate all the email functions of an online business.

Other Links