Some good web sites to check out are:

Hands-on Science Centers Worldwide
http://www.cs.cmu.edu/~mwm/sci.html

Science Centers with web sites
http://www.fi.edu/astc/trguide/websites.htm

Science Museums On-Line
http://red.www.nsf.gov/EHR/ESIE/museums.html

and of course, one of the most complete sites for museums in general is The
Guide to Museums and Cultural Resources at the L.A. Museum of Natural
History.
http://www.lam.mus.ca.us/webmuseums/main.shtml

Hope these help.
Larisa Overmier
Manager Museum-Ed
Project Assistant, Museum Management Consultants