Options-> Ring Tones/Alerts->Messages (might have to click it to expand) -> Email (mine has my gmail as the listed email)
From there you can turn on/off the LED as well as set custom rings.
The email listed under Email in that profile is my sprint.blackberry account and the LED is already set to Off. :/
Any other ideas?
With gmail app, you need to scroll down to other in that same section of the sound profile. There should be a choice for "Gmail - New Mail." You can control it there. The device doesn't consider mail coming in via the Gmail app to be new mail.