Windows only 
I’ve tried all kinds of Gmail notifiers in the past, and many of them leave something to be desired. I have to admit that one of the more recent ones, Spiffy, is on the verge of being awesome. Spiffy is simple, and that is partially because it is available in a portable form. The rest of the simplicity comes from being able to configure up to 5 Gmail accounts in a few minutes.
It doesn’t stop there though. You can configure all kinds of visual aspects including text colors/size in the popup alerts and the Gmail icon in the System Tray. One feature you might enjoy is something that can easily be overlooked, and it’s the ability to display notifications for specific labels in your Gmail account. That may not sound too useful, but it can be for some people. For example, I have a “Work” label in my Gmail account, and some of my emails bypass the inbox and go directly to that label. With Spiffy I can set up my work computer to notify me of new emails to that label, but at the same time they will be ignored by Spiffy running at home since I don’t have that configured to check the Work label. That way I only see those emails when I’m at work.
After you have Spiffy running I highly recommend perusing the customizations available. With some tweaks you’ll be able to get everything looking just the way you want it to.
For the geeks out there: On my machine Spiffy’s memory usage would top out around 3MB. So it’s pretty easy on resources, too.
Spiffy Homepage (Windows only; Freeware)
If anyone is looking for a good email notifier for Mac OS X, Notify is awesome. I’m currently using the free version. When you first install it, they give you 14 days of the paid version’s functionality.
Website: [vibealicious.com]
I purchased Notify for Mac as well – it is a great little app, and will hopefully continue to get better.
Excellent find Ryan!
Noticed the programmer has a forum but time is short… wish he could offer support for other email accounts (Yahoo, Live, GMX etc.).
There is one little app called UpdateWatcher that watches a lot of things, it supports multiple gmail and yahoo accounts.
Does Spiffy have a feature that will open GMail in its Chrome-created application shortcut when asked to open GMail to check new messages? This is the one feature that I have yet to find anywhere, and, as I’m testing the possibilities of using the GMail interface itself as a replacement for a desktop client, it’s this missing feature that makes GMail basically ineffective for that purpose.
I imagine it will open in whatever browser is the default on the system. Don’t most apps do that?
X-Notifier has that, and it has the ability to configure multiple accounts on gmail, yahoo, hotmail, gmx…. list goes on
In chrome, multiNotifier works pefect. It even takes me inside the GMail without the need to type in the username and password.
If other than GMail accounts are to configured, X-Notifier is the choice.