Marine Corps Marathon is a Great first-time marathon. It's mostly flat. There are few hills (there's one on thelast mile at the end which your adrenaline will carry you up), you'll have nice cool fall weather, LOUD supporters throughout the ENTIRE course as well as bands, and as an added bonus you'll get a great tour of the Smithsonians, Pentagon, National Mall, Monuments... can't beat it.

My first marathon will be Chicago in 2006. I have a friend who ran Chicago 2 years ago and said it was his best experience as far as the spectator crowd, the course (which, as I understand, if fairly flat), and the overall atmosphere of the race. Plus, since the race is in mid-October, the weather is cooler. Good luck on your first marathon!

Austin and Houston are two extremely flat/downhill marathons with great weather. I personally enjoy Austin the best as there is much to do outside of the race.

I've done both the Disney Marathon and the Marine Corp Marathon (mentioned above). I loved the Marine Corp marathon and have been disappointed in Disney. Disney is a flat course and even though you run through the parks, you spend the majority of the time on flat roads out in the middle of no where. Marine Corp kept me entertained for the entire race. Good course, lots of spectators, monuments, and marines taunting you. What a good day. The only downside is that you have to enter a lottery to get into it. Do so early to increase your chances.

Although I personally have never run this marathon, I've heard that the marathon in St. George, Utah is great. (However, it is quite popular and fills quickly. I believe it is run in October.) The course is downhill overall, so it is supposed to be a "fast" race. When I lived in Utah, many people that wanted to qualify for Boston or NY used this as their qualifying marathon. The race is in a very scenic area. Vegas is only about 1 1/2 hours away, or if you like National Parks, you can't beat the many options in Southern Utah. Good luck and Congrats on your first.

It's not Berlin, it's not Hawaii, but Detroit is a very nice first marathon. Flat, fast, friendly and international. After a quick trip through Corktown and Mexican town, you leave Detroit and enter Canada by the Ambassador Bridge (biggest "hill" on the course, but early in your run) run through a riverside sculpture park, and return to the U.S. via the Detroit-Windsor tunnel. Your Finisher's certificate will show your time for your "underwater mile." Back in Detroit, you run through the City's small, but growing entertainment district, and then to Belle Isle, Detroit's island park.
A quick tour of restored old homes in Indian Village,then back downtown, through Eastern Market and Greektown to the finish at Ford Field, home of the eternally hopeful Detroit Lions. First time marathoners get a special bib, and more cheers from the crowd -- guaranteed.

I would suggest finding a marathon with 10,000 runners or less. Smaller marathons make it easier for your supporters to see you on the route. In smaller marathons the group of runners spreads out at about 7 miles and it is more enjoyable.

I have done 17 marathons including Chicago 6 times. The earlier races were great because of the relatively small crowd. Last year in Chicago the route was almost as crowded at the finish as it was at the start. The crowd support is good and course flat but too many runners for me.

Grandma's Marathon in Duluth, MN takes place in June and it is a great route and not too hot at that time in MN.
Marine Corps is extremely well organized and great scenery.

I just completed Big Sur last April running from Big Sur to Carmel on the Pacific coast. It was awesome and a marathon you should consider in the future ( www.bsim.org)
It is quite challenging.

I will be doing Las Vegas this year.The route sounds exciting. Good luck.