Well, Bulgarian method executed as high levels of weightlifting is focused on extremely high frequency lifting... CNS acclimates fairly quickly producing pretty much insane strength gains. From what I've seen high frequency work does produce the fastest and best strength benefits in my own training as well. However, the one major problem I've run into and heard that athletes have run into with high frequency is overuse injuries.
As far as other types of programming there's all different types of periodization. A couple examples off the top of the head is Westside/conjugate method, concurrent, undulated, classical, etc. Here's a good article outlining a lot of the various "forms" of it that have developed.