Practically the only people in the world who don't suffer from e-mail overload are those who don't have access to e-mail. Almost everyone else, likely including you, are overwhelmed by the sheer volume of incoming e-mail, and have trouble prioritizing the onslaught. That's where EmailTray (formerly SenderOK) comes in.
EmailTray isn't a total solution to the problem, but it will certainly help. It lets you view and respond to what it considers high-priority mail--and you can view messages without having to open your e-mail client. Considering that it's free, you'll want to try it. It works only with Webmail accounts and Microsoft Outlook, though, so if you use another desktop client, you're out of luck.
Install EmailTray, and it indexes your e-mail in only a few minutes. Then it watches your inbox and displays the number of messages you've received in a system tray icon. Open EmailTray, and it displays all of your unread e-mail, by category: Top Priority, Low Priority, and those for which it was unable to assign a priority. It determines the important of an e-mail using an algorithm that takes a number of factors into account, such as how you previously interacted with the sender (if you responded, for example), and whether you recently visited the sender's domain.
You can read your e-mail from right within EmailTray, without having to open your mail client. You can respond to messages as well, although EmailTray will open your e-mail client to send a response.
What's particularly useful is that you can use EmailTray with multiple e-mail accounts, so that you can see all e-mail from all of your accounts in a single location.
EmailTray won't solve the problem of e-mail overload all by itself, but by alerting you when you've got new e-mail, and taking a first crack at telling you which messages are high priority, it will give you a head start.