A couple ways:
- Following developers online: Web developers like to talk about the tools they use… all you have to do is listen. Follow them online. Subscribe to their blogs. In fact, some blogs do nothing but open-source roundups.
- Word of mouth: Talk to open source people. Talk to them at meet ups, user groups, and conferences. Talk to them at work or over lunch. The more you talk, the more you'll hear the good resources come up again and again.