Keep in mind that "professional" needs to mean "functional" before "nice looking."
If you're using your iPad while sitting in meetings I highly recommend something like the Targus Versavue where you can rotate your iPad to portrait or landscape. The case comes in two flavors - with and without a keyboard.
If you're like me and you wander with your iPad, taking notes and checking research on the go, I recommend something like the Flexcase which gives you a handle on the back.