Hamilton - The Waterfall Capital of the World. - this website has a lot of information about all of the individual falls and their histories, and also posts notices of different events featuring the falls (like when they shine coloured lights on them!) and they host waterfall walks throughout the year. Definitely an excellent resource!
Cascades and Waterfalls of Hamilton - one of this site's best features is the way you can search for different waterfalls: by height, ease of access, area, height, type, and of course alphabetically. There are also some maps of the falls as well as cycling routes to a few of them, but they are a bit hard to decipher. This site is great for a cross-reference to find more technical information about the falls, how to get there, or surrounding attractions!
Great Lakes Waterfalls and Beyond - this site has a wealth of information! The author has visited many, many waterfalls and gives a personal account of their experience with it. This has waterfalls from Hamilton, the surrounding Great Lakes region, and a lot in the U.S. as well. If you want to visit some falls while travelling, this is a great site to consult!
Geotrail - Hamilton Waterfalls - features ten different hikes courtesy of Tourism Hamilton, with at least one waterfall on the way (sometimes more!) or different lookouts and points of interest. Shows the time, distance, and even altitudes of the hike along the way! A very useful resource for finding established trails, or if you want to check off a few waterfalls in one hike.
Secret Hamilton - for more awesome places and things to do around Hamilton!