Sync Outlook Contacts with Gmail and Google Voice...

With Go Contact Sync Mod sourceforge project... This little free app is easy to setup, it's lite yet featured, and it works well (being actively improved by it's developers). Go Contact Sync Mod can be ran manually, or can be configured to load on operating system start-up, synchronizing your Outlook contacts with your Google Gmail and Google Voice account contacts automatically. It's designed for Windows platform.

Go Contact Sync Mod

If you have Google Apps business account you may also want to check official  Google Apps Sync for Microsoft Outlook