This website does a fantastic job describing how rhythm can be created and utilized in a web design. Rhythm can be very effective in moving a user's eye across the website while also providing an aesthetically appealing appearance. Rhythm is an element that can tie an entire site together when used properly.
This You Tube video gives a tutorial of rhythm and repetition. It is very helpful because it explains the different elements and how they are used in the image to create rhythm and repetition.
I like this resource because it moves beyond the "whats" of repetition and rhythm and analyzes the real world effects it has and can be used for. (10/15)
Every week it never fails, any site with more visual examples of the design element is the easiest and sometimes quickest way for to fully grasp the concept of it.