For the past year (long before I actually had a job as a Montessori teacher), I have been collecting information and ideas from a variety of sources (mostly other teachers'/moms' weblogs). I have organized these various ideas to use in the classroom by storing them in separate "monthly" files on my computer. Using Microsoft Word, I organized the ideas by "areas" (i.e. practical life, math, language, science, art, music, etc.) in a document for each month. Then I printed each month's idea document and placed it in a binder in page protectors. I have separate binders for each month of the school year (however, I combined August/September). In addition to the idea documents, I have put any seasonal activities/materials that will fit into page protectors at the back of the binder. That way everything will be ready to pull out for that month and then can be filed back into the binder at the end of the month. This system will also allow me to easily add to each month's binder from year to year. Below I have posted some photos to show you what the system looks like.
Here are all the binders sitting in their box, ready to go to their new "home" (my new school) soon.
Here is a close-up of the labels I made for the spines of the binders.
Here is the first page of the August/September idea document to give you an idea of how I organized that part of each binder.
Here is one of the activities I have made for August/September. It is from the Kidssoup website. I am a member there and I highly recommend it. They have LOTS of great activities and games that could supplement the Montessori curriculum in many areas.