At 6'6" you're probably going to be looking at the top end of most manufacturers size ranges, road frames of 62cm and above are the range you'll be looking at.
I said "probably" though, you would do best getting yourself to a local shop that knows something about fitting people to frames.
Being so far from the average height I'd not risk buying something offline without having tried sitting on anything, particularly as it's your first road bike.
bicycles.stackexchange.com/users/2705/Iain M Norman
You really should go to a couple of good LBS's and get fit.
They'll be able to recommend some different companies that make bikes that will fit your build.
There are so many different variables besides just height that it's impossible to recommend a brand based on what you've given.
You need to know your stack and reach in order to find the best geometry for you.
bicycles.stackexchange.com/users/2701/Keith Rousseau
At 6'6", be wary of your local bike shop, unless you really trust them or they have a great reputation.
Sounds like blasphemy to say that, but one of the problems you may have is that many manufacturers may not make a large enough frame for you and you will get sold the biggest thing they have from the brands they carry.
Off the top of my head, in non-custom models, Trek and cannondale both make bikes large enough
(I have a 6'5" friend on both of those), and I know for sure Specialized and giant do not.
63+cm would probably be your likely range, but a good shop with a fit that you will probably pay 100$ or so for should be able to help you dial that in.
Things other than frame size are important as well.
I don't know your dimensions
but you're probably wider in the shoulders than most, so you'll want handlebars that fit you well.
Stem length is also partially driven by flexibility, so that's a consideration too.
Also crank arm length can be tough for bigger guys, the expert in tall bikes is probably Lennard Zinn.
He's a big guy himself and a custom frame builder, you may want to have a read through his site and consider some aftermarket options for those components.
bicycles.stackexchange.com/users/2760/conipto
Nothing "off the shelf" is going to fit perfectly for you.
To mitigate, you'll want to experiment with long seatposts that have set-backs and long stems.
Since you're a marathoner, you're probably quite fit and are limber enough to deal with handle bars that are far lower than the seat.
This lower stack height will also help you not be so cramped.
Eventually, you may want to get custom geometry ($$$), but tall folks can get by with frames that don't quite fit.
The pros do it all the time.
bicycles.stackexchange.com/users/1998/Angelo
SOMA makes good quality affordable frames and their ES comes in 66cm.
I'm only 6'4 but long in the limbs
and I rode that on an extended tour just fine.
The frame will probably set you back $400 or so which should leave room to kit it out.
bicycles.stackexchange.com/users/4126/Mike Samuel
Just about to ask a similar question, and figured I'd give you what I know so far.
I'm 6'8", more torso than legs.
36" inseam, 37" sleeve in dress shirts.
Trek 1.5 is the low-end Trek road bike, aluminum frame, and comes in a 64 or 65cm setup.
I have one.
It works pretty darn well, out of the box.
Both Trek and Specialized make bikes in this size, but not all of their bikes; that said, you're getting started around $1k.
Only change I made was upgrading the shifters on mine; they were terrible.
bicycles.stackexchange.com/users/12949/Dean J
I had a similar budget getting started and at 6'5" and change found it impossible to find a local bike shop that could find a good fitting bike.
I started out with the KHS Flite 747:
http://zinncycles.com/product/khs-flite-747/
You can get that for around $1600 and there are older models available for cheaper.
I measured myself and went with the XXL frame and then got fitted to the bike and
the guy said I fit the bike great.
I'm now looking into possibly upgrading with a http://bikeclydesdale.com/ which has bikes made for taller riders with more customizations.
bicycles.stackexchange.com/users/41524/Eric Worral
I'm a marathoner that is interested in mixing in some duathlons and triathlons, but I am having trouble finding a starter bike (< $1500) made for a tall man. I am 6'6". Any brands and models that you can recommend that offer a frame that fits someone around my height?
Starter Road Bike for Tall Man
bicycles.stackexchange.com
<road-bike><bike-fit><men-specific><tall>
bicycles.stackexchange.com/questions/6612
bicycles.stackexchange.com/users/2703/Zach Green
Finding a suitable bike for a very tall person can be quite difficult. It is probably a good idea to go to a local bike shop that knows something about fitting people to frames. Most people think that a frame size of 63+ cm would be right but it would be risky to buy something without sitting on it first. Lennard, Trek and Soma are manufacturers that specialize in bikes in larger sizes.  For bikes for taller riders that are more customizable, there is http://bikeclydesdale.com/ . There are many factors besides height that can affect the choice of frame, including shoulder width and reach. Good local bike shops will be able to measure you and fit you to a frame, but be wary of those that will try to give you the biggest frame they have, which may still be too small. Several brands make bikes that are suitable for taller riders, although models may be expensive. These include Trek, Cannondale, Leonard Zinn, SOMA, Specialized and Clydesdale.
Local bike shops may be able to fit you to a suitable frame, but since most manufacturers do not make such large frames and local shops do not stock them, be wary of shops that will just give you the biggest model they have. You need to consider variables in addition to height, such as shoulder width and reach. Longer seat posts with set-backs can help to increase the range of smaller frames. Several brands make bikes that are suitable for taller riders. These include Trek, Cannondale, Leonard Zinn, SOMA, Specialized and Clydesdale. In many cases, these can be quite expensive though.