Blue Ridge Marathon on the Parkway...I ran it last year and signed up for it this year. Just got reminded of it recently from looking at the Letsrun homepage and remembered how cool that marathon really was. Since then i've been excited to go to run it even though it's 4 months from now. It was extreamly well organized last year and the scenery was breathtaking.
One thing though is it has a lot of elevation change(over 3,000 feet of up and down and it literally drops 1,000 feet per mile for 3-4 miles). Probably why I loved it so much because I am amazingly good at downhill running and it doesn't affect my quads at all. I came within about 3 minutes of my pr on this course so it's obvious i'm probably a little biased on this one because courses like those I am really good at. Still though, if you ask anyone that ran it, they will probably all say the same thing. That it has amnazing scenery and is very challenging and the organization was great.
It's obviously not a very fast course for most people and not the best if your looking for a fast time but if your a good sub-elite runner(2:35-2:40 marathon time) it's a good race to get some pretty good rewards( watch valued at $5,000 but worth $1,500-$2,000 and a trip to Tucson for Mt.Lem Marathon). But in my opinion it's a good race and if your not looking for a fast time or don't care about the course and just want a pretty awesome marathon this is the one for you.
I also liked St.Jude Marathon, Disney Marathon(really cool one), Lake Tahoe Marathon and Triple, Boston Marathon(obviously the most prestigous and definately a must do marathon for any person who can get in), Exetur(Gansett), Rocket City, and Berlin are all really cool marathons.
The other three majors London, Chicago, and New York are really cool too. Houston is a nice marathon also. St.George is definately an amazing race just behind Boston in my books and really is a great great race and also a nearly completely downhill except some early hills and the course is very fast and enjoyable. Bay State is probably the best marathon in the world for a boston hopeful who is good at flat marathons. Tucson is fast and has a lot of downhill too but has been declining in quality recently. Twisted Ankle and Pikes Peak Marathons probably the best for the toughest marathons in the world. Followed most likely by some trail marathons and Mount Lemnom and maybe if your not a good downhill/ hill runner Blue Ridge.
Never do a Rock N' Roll Marathon in your life unless you are an elite who does sub-1:05-1:08 half or sub 2:20-2:25 full. You'll get big bucks if your an elite but they are horrible races for anyone who runs slower than those times. Mardi Gras Marathon is the only Rock N' Roll out of the ones i've done that even remotely is any good and really isn't all that great of a race..
I hope I gave you some options if you want to do a Spring or Fall Marathon or hoping for a variety of races or something like that, or are just curious. I have a ton of time on my hands so this at least helped take a slight bit of time. As you can see, I have a lot of races i've run and like, so I guess it depends on the person. But yeah, I would really suggest Blue Ridge. It's an awesome race so yeah.. Good luck if your going to do a marathon soon.