The Google Blog announced that Google Blog Search now supports the acceptance of pings. So when you add a new blog entry and you support RSS/XML/Atom you can send Google Blog Search a ping at their Blog Search Pinging Service. How do you do this? Well, you can read more at About Google Blog Search Pinging Service and view the Pinging API yourself. I tested it out on a different blog and got a 404, but it is very possible I pinged the wrong URL, I will test it again shortly.
Postscript From Danny:
Movable Type users want to put this:
into the "Others" box in the "Notify the following sites upon weblog updates" section of "New Entry Default Settings."
WordPress users, go to Options, Writing Options, the paste that line into your Update Services box.