If you use Google Voice, you are as annoyed as I am that gmail is push while Google Voice is polling-only. Here is a hack that allows you to get push notifications for Google Voice.
The way this works is it will forward the normal GV email notifications to a separate gmail box, which can be set up to push to the droid and have notification settings that are different from the normal settings (ie, a different ringtone)
From a PC:
1). Create a new gmail account that will just contain google voice notifications. I made mine be my primary email address, a period, and my google voice number.
2). In your primary gmail account (the one that receives google voice notifications), create two new gmail filters using the from addresses of txt.voice.google.com and firstname.lastname@example.org.
3). Set those filters to "Skip the Inbox (Archive)" and "Forward" to the new gmail account you just created.
From your Droid:
4). In the gmail app, go to "Accounts", "Add account", and add the new google account.
5). Change the notification settings for this account to be different than the other account (different ringtone)
Done! You now have a different ringtone depending on if you received an email or an email about an SMS or Voicemail.
1). If you want to change your notifications even more, try using 'Google Notifier' in the market. This will allow you to change the LED color and icon for the notifications. As a side-effect, this will also notify you for messages that skip the inbox as well as always notify you of new messages, even if you still have a pending notification.
Note: What I do is enable notifications in the gmail app for the primary account and disable them for the GV gmail account. I use "Gmail Notifier" to enable notifications for the gv gmail account and NOT the primary account. This way I don't get double-notification for the auto-archived google voice notifications.
2). Now that you have two gmail accounts, starting the gmail app will ask which account you want or go directly into the wrong account. To get around this, remove your gmail icon and replace it with a shortcut to your primary inbox, instead. (long press on home screen, select "Shortcuts", "Gmail label", and select the inbox of your primary account)
1). Notifications still show up as an email
2). No difference between SMS and Voicemail
3). No way to clear them out without manually clicking "clear" or reading the email.
4). This hack only makes sense until: Google Voice uses Push notifications or the gmail app allows per-label notification settings.
5). If you have a normal email notification waiting when you get a new google voice notification, it won't show up! Not sure yet if this is the fault of gmail notifier or the gmail app.