The best feature about Yahoo's webmaster tools -- called Site Explorer -- is the ability to upload links to all of your sitemaps and RSS feeds.

Site Explorer shows your top 10 queries with number of views and clicks. Yahoo's tool also shows you stats, for example, how many pages you have indexed and how many hosts/domains are linking to your site, but it doesn't show you the URL's.

This is my new favorite webmaster tool.

Enter the URL of the website you want to optimize for and then put in a target keyword. The results will show you two lists: the first will show you keywords and phrases related to your site and the second will show you keywords and phrases related to the keywords/phrase you entered.

Both lists will show you the monthly searches, the level of competition, and the suggested bid price (in Adwords) for each phrase. The first list will also show you the URL's where their suggested keywords came from (in your own site.)

This webmaster tool is very helpful in determining which keywords and phrases to try and optimize on your web page pages.

Bing's new webmaster tools help you monitor how Bing (Microsoft's search engine) sees your site content. You need to set up an account to get started, and then verify your site ownership by uploading a small file or meta tag to existing page. You can also provide the address of you online XML sitemap.

Once verified, Bing Webmaster Tools will show you a summary of your top 5 pages, crawl issues (if any), backlinks to your site (seems to show more than Google Webmaster Tools does), all of your outbound links, a keyword performance tool, and a ping tracker of your sitemaps.

So far, I am not finding the keyword tool very helpful. It just shows you solid bars if it finds your chosen keywords in your pages (and lists the pages) and does not show rankings. Perhaps this will be improved sometime soon.

Google Webmaster Tools is a very helpful way to monitor how Google is reading your website. After you have verified owner ship of your site by uploading a file or meta tag, you can provide the address to your xml sitemap and then monitor a number of things, including: top search queries, links to your site (often an incomplete list), crawl errors, keywords, and the status of your sitemap.

Google Webmaster Tools can help you tweak your robots.txt file so you can better control which files at your site should NOT be followed and indexed.

There is also a malware detector, crawl stats, HTML suggestions, and a site performance monitor that tells you how fast your site downloads in comparison to the rest of the world wide web.