http://www.stevia.net/ Hey, Sara,
I've used/use stevia and it is a good substitute to sugar or any other kind of sweetener....here's some info on it.
You can get it at a health food store, a bit pricey but....weigh the consequences. 
'A Powerfully Sweet Native Tradition'
The Guarani Indians had known for centuries about the unique advantages of kaa he-he (a native term which translates as "sweet herb") -- long before the invaders from the Old World were lured by the treasures of the New.
These native people knew the leaves of the wild stevia shrub (a perennial indigenous to the Amambay Mountain region) to have a sweetening power unlike anything else;
they commonly used the leaves to enhance the taste of bitter mate (a tea-like beverage) and medicinal potions, or simply chewed them for their sweet taste.
The widespread native use of stevia was chronicled by the Spaniards in historical documents preserved in the Paraguayan National Archives in Asuncion.
Historians noted that indigenous peoples had been sweetening herbal teas with stevia leaves "since ancient times." In due course, it was introduced to settlers.
By the 1800s, daily stevia consumption had become well entrenched throughout the region -- not just in Paraguay, but also in neighboring Brazil and Argentina.
Like the discovery of America itself, however, credit for stevia's "discovery" goes to an Italian. In this case, the explorer was a botanist whose initial unfamiliarity with the region (along with his difficulty in locating the herb) caused him to believe that he had stumbled onto a "little-known" plant.
A New World "Discovery"
Dr. Moises Santiago Bertoni, director of the College of Agriculture in Asuncion, first learned of what he described as "this very strange plant" from Indian guides while exploring Paraguay's eastern forests in 1887.
This area was not the herb's native 'growing ground.' Consequently, Bertoni, by his own account, was initially "unable to find it."
It was 12 years before he was presented with tangible evidence -- a packet of stevia fragments and broken leaves received from a friend who had gotten them from the mate plantations in the northeast.
He subsequently announced his discovery of the "new species" in a botanical journal published in Asuncion.
Bertoni named the "new" variety of the Stevia genus in honor of a Paraguayan chemist named Rebaudi who subsequently became the first to extract the plant's sweet constituent.
"In placing in the mouth the smallest particle of any portion of the leaf or twig," Bertoni wrote, "one is surprised at the strange and extreme sweetness contained therein.
A fragment of the leaf only a few square millimeters in size suffices to keep the mouth sweet for an hour; a few small leaves are sufficient to sweeten a strong cup of coffee or tea."
Probably more info then you wanted to know, but that's the scoop 
Help this helps,
-laserred-