The Opera browser has had an excellent integrated email and news client for a very long time, but it's now becoming a separate product, Opera Mail, which you can download and use on its own.
The program can be used with all the main email services - Gmail, Hotmail, Yahoo! Mail, MobileMe, AOL Mail and more - along with anything else which provides IMAP or POP access to your inbox.
Setup is easy. A straightforward wizard helps you import accounts from Opera, Eudora, Thunderbird, Outlook Express and so on. Or you can create an account manually by specifying your logon information, server details and so on. Either way, once configuration is complete you'll immediately be able to send and receive messages.
Opera Mail works a little differently to other email clients in some ways. It doesn't save your messages into separate folders, for instance; instead they stay in a single database, and can be organised and filtered by a series of Views. And you can then open and access messages via a convenient tabbed interface, particularly useful when you need to look back over a series of emails.
All of this is reasonably straightforward, though, and shouldn't hold you up in any way. Just click the Opera Mail button for a menu which provides easy access to everything you want to do. And if you do need more help, double-click the "Welcome to Opera Mail" message in your Received view for links to various helpful tutorial and support pages.
Note this is the portable version of Opera Mail.