Many schools have extensive demonstration website were many useful ideas can be found. A few useful ones are listed below. Each of them has links to many other great sites.
The University of Maryland
The University of Virginia
Wake Forrest University
North Carolina State University
Montana State University
Universoty of Southern California
Michigan Technological University
University of Colorado
A great search engine can be found at http://physicslearning.colorado.edu:9999/vestris/QuerySp.html that indexes 39 different demonstration sites.
The Physics Instructional Resource Association (PIRA) has compiled a list of many standard physics demonstrations and an indexing system (DCS) to give a standard name to the demonstrations. Members of PIRA also maintain a webring of websites that support physics teaching. PIRA members also maintain a listserve (TAP-L) that support discussion of physics teaching.
Virginia Tech Physics Lecture demo list