I buy liquid Stevia Glycerite by NOW. Each stevia brand tastes a little different, so you may want to try it before stocking up. I get an 8 oz bottle from Amazon.com which costs about 50 percent less per oz than the 2 oz bottles in the health food store. I haven't used it in cooking, but I make iced tea with it all the time. I boil a half a gallon of water and soak four tea bags for 5 minutes. I then add 1/4 cup of sugar and 1/2 tsp. of stevia. It reduces the calorie count per glass to almost nothing, if that's a concern for you.
Stevia alone is too bitter for me. Many people can use the powered form, but I find that to be horrible. The 8 oz bottle of liquid stevia lasts me about 9 months. I live alone. Iced tea is my regular beverage along with hot tea and water.
I haven't used stevia in cooking, but I know there are cookbooks that specifically use stevia as the sweetener.
I'm sure others will give you more information. Good luck in your search.