What you need is a pinging plugin. Pings send the spiders to check out your new posts. I use MaxBlog Press ping optimizer, because it prevents the overpinging that can get you into trouble.

If you need any help, just send me a PM.

Edit: Another good plugin is Google XML Sitemaps.

Here's the description:

This plugin will generate a special XML sitemap which will help search engines like Google, Bing, Yahoo and Ask.com to better index your blog. With such a sitemap, it's much easier for the crawlers to see the complete structure of your site and retrieve it more efficiently. The plugin supports all kinds of WordPress generated pages as well as custom URLs. Additionally it notifies all major search engines every time you create a post about the new content.

WP automatically pings pingomatic . com, which in turn pings a bunch of other sites.

IF its a new blog, then I'd recommend you Social bookmark your site on Digg and sites like Jumptags, Fold etc.

Once your site is indexed and you want to add content, XML Sitemaps is great but you can do the following to;

Go to settings > writing > and in the 'Update Services' box, paste in the following;

http://rpc.pingomatic.com
http://www.blogpeople.net/servlet/weblogUpdates
http://ping.myblog.jp
http://ping.bloggers.jp/rpc/
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My new content is indexed within 1 minute of me adding the content and I've tried this on over 30 different WP blogs.

Hope that helps

Zaher