Bernard - All the top open-source ERP products come with full-featured accounting modules. Do you require some functionality that a basic feature set can't provide? I've heard good things about OpenERP, Openbravo, and xTuple, so check those out. Opentaps and PostBooks also look interesting, but I don't have any firsthand (or secondhand) experience with them.
xTuple and PostBooks are the same thing. There is all kinds of information including documentation, videos, and of course the software, at www.xtuple.com.
In addition to the ones mentioned below, you could look into WebERP.