How can I get an email message's text content using Python?

In a multipart e-mail, email.message.Message.get_payload() returns a list with one item for each part. The easiest way is to walk the message and get the payload on each part:

import email
msg = email.message_from_string(raw_message)
for part in msg.walk():
    # each part is a either non-multipart, or another multipart message
    # that contains further parts... Message is organized like a tree
    if part.get_content_type() == 'text/plain':
        print part.get_payload() # prints the raw text

For a non-multipart message, no need to do all the walking. You can go straight to get_payload(), regardless of content_type.

msg = email.message_from_string(raw_message)
msg.get_payload()

If the content is encoded, you need to pass None as the first parameter to get_payload(), followed by True (the decode flag is the second parameter). For example, suppose that my e-mail contains an MS Word document attachment:

msg = email.message_from_string(raw_message)
for part in msg.walk():
    if part.get_content_type() == 'application/msword':
        name = part.get_param('name') or 'MyDoc.doc'
        f = open(name, 'wb')
        f.write(part.get_payload(None, True)) # You need None as the first param
                                              # because part.is_multipart() 
                                              # is False
        f.close()

As for getting a reasonable plain-text approximation of an HTML part, I've found that html2text works pretty darn well.