I believe Google has a Gmail gadget for your iGoogle page available at this link - http://www.google.com/ig/adde?moduleurl=builtin_gmail.xml&source=imag
you can also search for gadgets with the term "check email"
Be warned, that there might be some unscrupulous / malicious code out there.
Ideally, if it's only notification you want, use official notifiers from service providers or an offline client. Preferably, one that connects securely.
You could simply embed http://m.gmail.com in an iframe. Gmail also offers RSS feeds, but only for unread mail and it's a password-protected feed.