A very good pumpkin beer is Dogfish Head's Punkin (and yes, that's spelled correctly) Ale. There are a lot of pumpkin ales out there, but this is truly one of the best. It't a high quality brown ale, with pumpkin mixed in along with some seasonal spices. It is pumpkiny, but not over the top in an artificial manner.
The downside? While you can get it all of the Northeast (and I believe the country), the price goes up the further you get from Deleware. I got it for $42 a case in Philadelphia. The other problem? They only make a limited amount. The distributor I got it from was only able to get 5 cases for the entire year, despite wanting to get more.
But if you can get your hands on it and don't mind dropping some money, it's pretty good stuff. Plus, while $42 a case sounds expensive, that's still less than $2 a beer. You probably wouldn't blink to pay more than that for a Miller Lite at a bar.