Zotero is a free web-based plug-in that provides an alternative for collecting, managing, and citing research sources.
DOIs (Digital Object Identifiers) are used to identify digital materials uniquely and persistently. APA is now recommending that these numbers, when available, be included in citations to electronically retrieved articles. Many articles indexed in PsycINFO and other databases now include DOI numbers. Here is an example of the use of a DOI number in a citation:
Padilla-Walker, L. M., & Carlo, G. (2007). Personal values as a mediator between parent and peer expectations and adolescent behaviors. Journal of Family Psychology, 21(3) 538-541. doi:10.1037/0893-3220.127.116.118