Google Voice Desktop Notifier
This is a simple Chrome extension that polls Google Voice and shows a desktop notification when new messages arrive.
Note: This extension is not my original work, it is a modification of an existing extension, Mini Voice (Chrome Store link). Mini Voice does the same thing, only with a badge notification next to the address bar.
Install Google Voice Desktop Notifier (Web Store link) extension from the Chrome Web Store.
The extension runs in the background, there is no indication of it running except for when a new message arrives. I use it in addition to the official Google Voice extension. GV Desktop Notifier alerts me of new messages, and I view them by clicking on the icon next to the address bar.
You can also click on the notification to open Google Voice in a new tab.