JabRef
JabRef is a Grafical User Interface (GUI) to manage BibTex databases. There are two things that makes this program very useful and intersting: is a java jar file, which means you can run it in different platforms and save all data in a bibtex file format. In addition, this progam is free software.
JabRef allows you: Import old bibtex files (you don't need to reenter all you bibliography). Fetch papers/books/... references directly from [1]MedLine and other databases. Import references from IsiKnowledge (not directly like MedLine)