Juice from red cabbage. It turns blue in a basic solution. Even green when the pH is high enough. You can also use juice from almost any red flower or fruit like roses or cherry's.
pH strips are used to determine whether a solution is acidic or basic
Lugol's Iodine is used to detect starch in a solution. Benedict's is used to detect simple sugars (glucose) in a solution.
biuret reagent
http://www.chemheritage.org/educationalservices/pharm/tg/chemo/activity/vitaminc.htm
Purple blue at pH > 8.2 to 10. However pH higher than 13 will discolorise in some time.