- Go to: https://www.google.com/webmasters/tools/ and log in
- If you haven't already, add and verify the site with the "Add a Site" button
- Click on the site name for the one you want to manage
- Click Health -> Fetch as Google
- Optional: if you want to go a specific page only, type in the URL
- Click Fetch
- Click Submit to Index
- Select either "URL" or "URL and all linked pages"
- Click OK and you're done.
Your second (and generally slower) option is, as seanbreeden pointed out, submitting here: http://www.google.com/addurl/