I have been searching for the most cost effective way to go around the world. I am starting in the States, traveling to Europe, Africa, Asia, Australia and then to South America. Much of my travel will be overland, but I need to be able to fly from continent to continent to complete the trip in a year. I have seen a lot of deals on line and gotten some good advice on the thorn tree, but I have not seen anyone talk about AirTreks.com. If anyone knows anything about this company or has used them, if I could have some advice that would be stellar. Thanks

I've used them a few times, no major complaints.
Check around, though, because sometimes the airline alliance RTW fares can be cheaper (or more flexible) than what AirTreks will recommend.
And if you're doing a lot of overland travel, you may be better off picking up one-way tickets as you go. Contrary to popular myth, they often aren't that expensive, especially as you get away from the US and Europe.

we found that Air treks were really expensive They gave us a price and said it was the best deal around. I am also from the states and just did a RTW. We used frequent flyer miles and got to Europe. We baught our RTW tickets from STA in london and ditched our last flight when we got home to Seattle. we saved over 1000 us on each ticket by doing this.
The one way option could be a better way to do it also . It just depends on your flexibility of you plans. A RTW tickets is good if you have fixed dates and know what you really want to do and where you want to go. ( our option) One ways are good if you just want to go with the flow.
Enjoy the trip

One of the cheapest RTW there is is the Escapade, you can use Virgin Atlantic/Air New Zealand/Singapore/Silk Air on it.
You can do most of your itinerary with it, US to Europe with Virgin (London only though), Virgin again down to Africa (South Africa/Kenya only), Africa to Asia on Singapore Airlines then off to OZ with them again. Then from OZ to South America, you can go via Auckland to Santiago with Air New Zealand (a code share with Lan Chile so not entirely sure if you can use that particular flight I have to admit).
You'll have to travel overland back to the US though.
Another option would be to fly straight back from OZ to the us on that Escapade ticket and travel to South America separately.
The fare is usually around £800 plus about £200 taxes so about $2000 I reckon.
For a bit more you can do a One World with British Airways/American airlines/Qantas/Iberia
I'd speak to STA travel if I were you, they must be used to selling RTW, good luck!!