Bike shorts. You can also just get liners to put under regular shorts if you're not excited about wearing skin tight lycra in the great outdoors... mountain bike shorts are a sort of cross between the two I think.
Chamois cream is good for moisture control on long rides, so I don't bother with it for anything less than 70 miles or so but feel free to try some out if you think it will help you.
And no underwear under the bike shorts.
