I have not read the other responses, but don't let anybody pressure you to stop breastfeeding your toddler. It's not totally accepted in this culture to nurse a toddler, so you are fighting people's perceptions and cultural norms; however, your child's health and what works for your family is paramount.
I nursed one daughter to 17 months and the second to 29 months. I never expected to nurse past two years, but she loved it so much and it worked for us. Plus, I knew the benefits of nursing toddlers (discovered them with my first who never had an ear infection or allergic reaction until after I weaned her.)
They are both fun, independent, very intelligent little girls who are not clingy or developmentally stunted due to extended breastfeeding.
I believe a mother should breastfeed for as long as she and her child mutually agree upon it. That is to say, if one of you really wants to stop, it's time to stop. If both of you are happy to continue nursing, it's nobody else's business to tell you to stop.
Here are a couple of article I have written on the topic:
Nutritional Benefits of Breastfeeding Toddlers: http://breastfeeding.suite101.com/article.cfm/nutritional...
Mental and Emotional Benefits: http://breastfeeding.suite101.com/article.cfm/extended_nu...
Whatever you decide, your son is a lucky little boy for being breastfed by a dedicated mom for over a year. :) Enjoy your little boy.