My home"brew" solution, which works, but is not exactly elegant.
I had high hopes for this bottle from Thermos, because it has a lid that completely covers the drinking hole. Unfortunately it's too narrow for the bike holder, and slips through the ring! I tried another Thermos brand mug, and it leaked the first time I hit a bump, and I had to dig the plastic bag I keep under my saddle as a rain cover out to keep it from splattering on me the whole ride.
Do you ride with a cup of coffee onboard? Is it part of your daily routine? What's your system for portage?