In my eleven years of designing, developing and maintaining websites, I've come across many sites/tools that offer value to webmasters. Though I have a large list of bookmarks, I have narrowed it down to twelve [free] sites that I find to be the most useful, and I visit them often. I'll list all twelve here. (I originally planned to write about ten tools, but I found there were two more I just couldn't leave out) I'm not listing them in order of relative importance, but rather in the order in which you'd go to them when creating a new website.
1. Overture's Keyword Selector Tool
When you're in the planning stage for your site, this will help you validate whether or not your idea is a good one. It will tell the estimated number of times that term was searched on in the last month, so you'll be able to get an idea of how in demand your site will be. It also provides related searches that include your term, which give you an idea of the content to include in your site.
2. Pre-built PHP Scripts
This site can save you a lot of time and money, in that you won't have to develop your site from scratch. Whether you're looking to implement a CMS or blogging tool, or perhaps including classifieds or a photo gallery, the free scripts on this site will prevent you from having to build from scratch.
3. Current web design style guide
This will give you many ideas and considerations when creating the actual template for your site.
4. CSS Tools
When you're designing your template based on item #2, you'll most likely need some CSS help. OK, so this link is actually to another list, but it's certainly an incredibly valuable and comprehensive one. If you have any question about CSS or would like help creating an effect on your site that you've seen on another, you'll most likely find the information there!
5. A Color Matching Tool
Unless you're an artist or very good designer, you may not instinctively know which colors work best with each other. So if your logo contains primarily #80ABBF blue, and you want to design your template around it, this site will help you find complimentary colors to incorporate into the design.
6. Favicon Editor & Generator
While this is not absolutely essential, it's becoming more common practice to for sites to have a custom favicon. (If you're not sure what that is, it's the little icon that appears beside the URL, the title in the tab, and the favorite/bookmark, depending on your browser. It gives your site a professional, fully-developed feel. You can 'draw' your own with this tool, or upload a 16×16 .png file to generate your custom favicon.ico file.
7. Free Stock Images
This is an enormous resource for those who want to place professional looking photos on their site, but don't want to pay the normally high price for stock photos. Alternately, I'd recommend iStockPhoto for very cheap stock imagery.
8. Search Engine Submission
Once your site has some structure and content, it's time to alert the search engines, and start drawing traffic! Here are quick links to the top three, you're on your own to find others…
9. Sitemap Generator
To have your site indexed more quickly, regularly and completely, you need an XML sitemap that conforms to the current sitemaps protocol. If you have Joomla, WordPress or another CMS, you can most likely find a plugin that automatically generates your sitemap. Otherwise, use this tool to manually spider your site and create one for you.
10. Web Analytics
While you may have free web analytics tools that come with your hosting package, Google Analytics will give you insight into your visitors and their navigation on your site that simply can't be rivaled by any other free tools.
11. Search Ranking and Back-link Monitoring Tool
As your site grows, you can use this tool to monitor how you're tracking in search rankings for your keywords. You can also see how many backlinks your site has, and how many pages the search engines have indexed on your site.
12. Webmaster Forums
Join these forums, and you'll never look back! Here you'll find invaluable advice from thousands of other webmasters on how to continually improve your site, and increase traffic and profits from virtually any type of site!