First try the definitive site, www.TimHunkin.com and the specific pages on that site here. 

Also the Secret Life Of Machines Episode Guide is excellent. This is the place to go for a guide to each episode listing models, machines, guests, and films used, plus stuff about the theme music, and more...

We also recommend the excellent Science Zero website.

Of course new sites and discussion group topics come up all the time, so the best thing to do is to use a search engine to see what's new... try clicking on either of these links http://www.google.com/search?q=secret+life+of+machines and http://search.aol.com/dirsearch.adp?query=secret+life+of+machines