Make Gmail use SSL
The tip of the day of the week of the year of the month comes from the guys over at Mac Os X Hints.
Basically, take the normal gmail url: http://mail.google.com and change it to https://mail.google.com to force Gmail to use SSL. I have no idea why they don't do this to begin with, but they don't. Anyway, that should make your email a tad more secure when using wireless.