I've configured the CNAME records for mail so that I can access a simple sub-domain as I would for any other webmail interface.
I've never seen a list of valid CNAME entries other than "mail" for the google apps by the way. Even in Google's own documentation all I've ever seen given was an example of how to set mail. Without the correct name to create a record for, the fact that it can be done is sort of moot.
But what Google is also lacking is an easy way to get to their Apps product page and then a simple login link from there. They do have a product page here:
http://www.google.com/apps/index.html But there's no link TO this page (Apps) from google.com for example.
And from there you then have to click on BUSINESS to get to here:
http://www.google.com/apps/intl/en/business/index.html#utm_medium=et&utm_source=catch_allWhich is a more graphical product page. Which then has a small "returning user?" prompt where you can click to log in.
The other issue is that they don't offer a one-stop login page for all GMAIL users while doing the redirection on their end. That is to say, I've had to tell a few people multiple times to make sure NOT to go to gmail.com even though they are using gmail as part of our webmail. They may have wanted to brand it differently or allowed rebranding.