Gmail Fetcher

I am a hard working Google saleman and goes around to persuade people switch to Google and of course, Gmail is one of the product that people accept most. However, same as switching to other email clients, it is a headache to manage all of the accounts at one go. Though you can customise the 'From:' address in Gmail, you still can't receive emails from other clients like Yahoo and MSN. Now, it is possible. Gmail Fetcher allows users to fetch emails from other email clients via POP3. Here are a few things you can do with the incoming emails (Quote from Gmail Help Center):

• Leave a copy of retrieved messages on the server. If you'll only be accessing your email through your Gmail account, leave this unchecked. If you'd like to be able to access your mail directly from that account, or if you're accessing it through any other accounts or devices, click to select this option.
• Always use a secure connection (SSL) when retrieving mail.
• Label incoming messages. If you'd like to automatically label all messages that are retrieved from your non-Gmail account, select this option. You can choose to use the predefined label (your email address), or you can select an existing label or create a new one from the drop-down list.
• Archive incoming messages. Mail from this account can be archived directly, without showing up in your Inbox.

Here is the official description from the Gmail 'What's New' page:

Get mail from other accounts
Now Gmail can check for the mail you receive at your other email accounts. You can retrieve your mail (new and old) from up to five other email accounts and have them all in Gmail. Then you can even create a customized 'From:' address, which lets you send messages from Gmail, but have them look like they were sent from another one of your email accounts. Please note that you can only retrieve mail from accounts that have POP3 access enabled. Learn more

This feature is currently only enabled for a limited number of users. I suppose you will see the 'New Feature!' link at the top right corner of your Gmail homepage if the feature if available to you. You can also look for it in the 'Accounts' tab in Settings.