We just completed a kitchen reno and had granite countertops installed. My countertops were sealed and came with instructions to not use any cleaning products with citrus, ammonia or bleach. I saw a number of different granite cleaners available at the supermarket and BB&B, so I Googled a bit to find out more about the "best" one to use, and came across a couple of websites that recommended variations of a homemade recipe. I figured I'd try it out and I'm really happy with the results, so I thought it was worth sharing:
1/4 cup of rubbing alcohol
5 drops of Dawn or other dish soap (Castile soap would also be a good alternative if you prefer)
5-10 drops essential oil (optional – to help mask the alcohol smell -- I used lavender because I happened to have it in the house)
1 3/4 cups water
-- Put the rubbing alcohol into a 16 oz spray bottle.
-- Add the dish soap and essential oil
-- Fill up the rest of the bottle with water.
-- Shake the bottle gently to mix the ingredients.
To use it, spray it onto the countertops and wipe off with a microfiber or other soft cloth. It should give your countertops a nice, clean shine. As a bonus, it works well on stainless appliances, too. It cleans well and dries streak-free, it smells nice and costs a fraction of the store-bought stuff.