I won't publish the recipe here, but if you subscribe to Cook's Illustrated online, you can find the best chocolate bundt cake I've ever had. It has semisweet chocolate and cocoa in it (and butter and sour cream*), and gets better with time. I made one for work the other day. My husband and I tried a cupcake we had made just for tasting purposes the night I made it, and it was good. The next day at work, the cake was better. And one of my colleagues took a bite in the morning, then saved the rest for after lunch, and he told me after lunch it was even better.
Cooks Illustrated will give you a 14-day free trial before you have to pay for the content. The recipe is called "Chocolate Sour Cream Bundt Cake."
Cook's also tested a number of Bundt pans. I asked for, and got, a Nordicware Bundt pan for Christmas, and it is awsome. The cake came out of the pan looking perfect.
*note: I didn't have any sour cream on hand so I used yogurt. It came out fine.
Lecithin-free semi-sweet chocolate or bittersweet chocolate bars (two 3-oz bars)