There are many gmail enhancers/web apps out there. Some of them are listed below that can greatly help you in reducing your time to groom or manage your gmail account.
This web app will organize your gmail inbox. It automatically analyzes your incoming mail, label and archive low priority emails. Other Inbox will make sure that Your important emails sent by real people are left in your Inbox.
Are you flooded with email from email marketers? You still receive emails from email marketers even though you unsubscribed from their services? then check out Unsubscribe web app for gmail. It is available for other emails such as Yahoo Mail, Windows Live Mail etc.
Are you running out of free space in your gmail account? Then have a look at FindBigMails web app. Gives you a comprehensive graphic details of usage details, large emails etc.
Rapportive finds relevant information about your contacts, email senders from social media and builds a rich contact profiles right inside Gmail. Rapportive shows you everything about your contacts right inside your inbox.
AwayFind escalates your urgent emails when you are away from it. When you receive an urgent message, AwayFind will notify you via SMS, voice call, iPhone push, IM, or even delegate the message to someone you specify.
See if you email gets read or not and when!
Labnol (a technology blog) has a decent article on how to use Hotmail as an alternative backup place for your gmail mails!
Connect TripIt to your gmail! It automatically polls your inbox, scanes for travel emails, forwards it to your tripit mail so that your travel plans are automatically scanned, and then sent to tripit. Great tool.
Compose an email in gmail and then schedule it to be sent later! cool email scheduler program for gmail.