Google says wordpress automatically submits new domains to them. I'd love to use the same technique in another system, but cannot find any documentation on how to do this.
When my WordPress site sends out the ping, Googlebot usually comes to crawl the new page within a couple minutes and often chooses to index that page within a day. For new sites, Googlebot will probably come crawl right away, but it will usually take longer for Google to decide to index content that it finds.
There are other ways to alert Google to new sites. One of the best ways is to create a link to it somewhere. It may take Googlebot a couple weeks to re-crawl the page with the link and follow it, but the link passes some authority to the page which makes it more likely that Google will decide to index the content.
I've also seen evidence that Google subscribes to feeds of newly registered domain names and automatically tries to crawl freshly registered domains. Because, of this, you probably don't need to submit a new site to Google at all. Google will know about the site from its domain registration.