- Zotero.org is a plugin to Firefox. It's open source and has lots of nice features but sharing is not yet developed.
- Citeulike.org is a web-based interface that allows open sharing of pages.
However, it exports only in RIS (e.g. for Endnote+Word) or Bibtex (for Latex). What should I use if I want to use OpenOffice or just html for my documents?
Create a new Citeyoulike group for each document, and to simply link to that at the end of each online document. When a paper needs to be finalised one can export the list into a completed Endnote file, and thence to the format required in the paper.