[Air-L] Can someone point me to a good open source reference citation program that works?

Can someone point me to a good open source reference citation and formatting program that works and is easy to use? I write a lot but I find myself cut in the web of digging through several manuscripts to locate sources and then having to having to cut and paste which is inefficient. My primary concern is for APA style but I will not mind one that can do APA and Chicago or MLA or their combo. Thanks in advance Oh by the way I'm using MS word 2003. Bolanle