SOLVED: Different sounds for different email accounts
I finally found a partial way to do this on my D2 with GMail 2.3 installed.
For anyone who cares:
My setup:
D2 running the latest 2.2, rooted but no custom ROM or anything
No email clients installed other than an updated GMail client and the stock client
Main email account is a corporate exchange account
Two other mail accounts are configured, both using GMail
Standard D2 blur
First, I set the default notification for the whole phone to something reasonable.
Then, I opened the GMail application (not the universal inbox, not some other email client) and selected my first account, hit the settings button bringing up the menu at the bottom of the screen and tap "More". Then tap "Settings".
The resulting settings menu it shows has the gmail email address up in the top right portion of the screen, which (I believe) implies that the settings being edited are specific to the selected account. You can scroll down, tap "Select ringtone", and choose the ringtone you want for the account.
Then, I backed out and selected my second account and did the same thing for it but selecting a different ringtone than the first.
Note: I believe, but I'm not 100% sure, that my second account may have also accepted the change that I applied to the first--when I went to select ringtone for the second account, I think it had changed to what I selected for the first account making me think that the setting I edited for the first account was a more global setting. Going back and forth between accounts after setting the ringtones, however, showed that the individual accounts maintained their own settings. Bingo!
So far this is working perfectly for me.