This is mainly for my own info, but I hope you find it useful for submitting your own site.

http://www.ysearchblog.com/archives/000437.html

All search crawlers recognize robots.txt, so it seemed like a good idea to use that mechanism to allow webmasters to share their Sitemaps. You agreed and encouraged us to allow robots.txt discovery of Sitemaps on our suggestion board. We took the idea to Google and Microsoft and are happy to announce today that you can now find your sitemaps in a uniform way across all participating engines. To do this, simply add the following line to your robots.txt file:

Sitemap: http://www.example.com/sitemap.xml

Please provide the complete URL for your Sitemap on this line. We will pick it up wherever you put it in your robots.txt file. This directive is not specific to user-agent. If you have multiple Sitemaps, you can point to your Sitemap index file on this line. Details about the Sitemaps protocol including this addition are available on the protocol website — http://www.sitemaps.org.

http://blogs.msdn.com/livesearch/archive/2007/04/11/discovering-sitemaps.aspx

Today, I’m happy to announce the latest addition to the protocol: Sitemap Autodiscovery. Autodiscovery gives siteowners the ability to easily share their sitemaps with all search engines at once, without the overhead of manually submitting them to each one. In order to share your sitemap with the crawlers at large, you simply provide the following line in your robots.txt file:

Sitemap:

Where is the complete URL of your Sitemap Index File (or your sitemap file, if you don’t have an index file). This directive is independent of the user-agent. so as long as it is present in the robots.txt file, all engines will be able to find your sitemaps. I see this as an important extension to the protocol, as it removes the need to individually submit sitemaps to each engine - simply add one line to your robots.txt file, and we will find your new and updated sitemaps automatically.

http://about.ask.com/en/docs/about/webmasters.shtml#22

Q: Does Ask.com support sitemaps?
A: Yes, Ask.com supports the open-format Sitemaps protocol. Once you have prepared the sitemap, add the sitemap auto-discovery directive to robots.txt as follows:

SITEMAP: http://www.the URL of your sitemap here.xml

The sitemap location should be the full sitemap URL. Alternatively, you can also submit your sitemap through the ping URL:

http://submissions.ask.com/ping?sitemap=http%3A//www.the URL of your sitemap here.xml

There is also this page which allegedly submits your sitemap manually to the big 4
http://www.mypagerank.net/service_sn_index

See also
http://www.google.com/analytics/
http://www.google.com/webmasters/
http://www.google.com/addurl/?continue=/addurl
https://siteexplorer.search.yahoo.com/

And if you DO add that line to robots.txt (which is fairly essential) then you need to check you did it OK with this tool
http://tool.motoricerca.info/robots-checker.phtml