The internet version of the daily newspaper Haaretz contains a lot of information about volunteering opportunities in Tel Aviv:
The “Volunteering in Israel” internet portal is intended to centralize the extensive information which exists about volunteering in Israel. The site allows the public to access information about the various volunteering organizations and the existing opportunities to which one can volunteer.
Volunteers for Israel (VFI) is a non-political, non-profit, volunteer organization.
Originally created to help deal with the shortage of manpower during the war in Lebanon the program's network now extends to 36 countries and over 100,000 volunteers have served with the aim of building bonds and solidarity between the volunteers and Israelis, of intensifying the Jewish identity of Jewish youth living outside Israel, and is intended for those that want to contribute to the state of Israel in a personal way.
The Israeli Ministry of Foreign Affairs http://www.israel-mfa.gov.il/archdigs.html lists archaeological excavations throughout Israel that are looking for paying volunteers. Applications should be made directly to the archaeologists leading the digs.
Consider also the Israel Youth Hostels Association, International Convention Center, P.O. Box 6001, Jerusalem 91060, Israel; 011-972-2-6558400; email@example.com. They are often in need of volunteers to work in their hostels throughout the country.
Amirim is a summer volunteering program for college students and young professionals aged 18-35. Through your work at a non-profit organization you will have the opportunity of discovering Israel, its culture and society.