You've got options! - Sweetner for Tea by: Samy St Clair
Stevia is a wonderful sweet herb that can be added to any blend. It can be purchased as both a bulk herb or in a powder form at most health food related stores.
Another option and possibly my favorite is Agave Nectar. It's a natural, low glycemic index substance that is harvested from an Agave plant. The taste is very sweet and very light, making it perfect for a delicate tea blend. This too is available at health food stores everywhere as well as online. I've also seen availability growing at your standard grocery store, usually close to the honey.
Honey is the third and possibly most popular sweetening agent outside of white sugar for tea. It's usually a perfect choice for tea as it's rich flavor and health benefits tend to compliment tea in a way that makes me suspect they where made for each other! A little tip with honey is always go local. Aside from the obvious benefits of supporting local businesses, the pollens in the honey have also been known to help your body acclimate to pollen related allergens. This is a tasty way to naturally build your own immunity to local pollens.