Makhane Yehuda (the Jewish Camp, "מחנה יהודה")
According to a Jewish tradition the street vendors have to leave the produce they can't sell anymore to the poor. So at the end of the market (which is pretty late, around 20:30 or so) you can find tons of good food. On Fridays the market closes earlier because of the Shabbat, around 16:30.
"Ginger" (zangvil, זנגביל) Vegetarian Community Center
The Community Center holds a free market once a month on the first Friday of each month. You can bring, take or exchange whatever you want (or do not want anymore). "The junk is always greener on the other side".
Address: Balfur 8, starts at 11:00 am.
Official site: www.ginger.org.il