What you will find in every Montessori Classroom
Every classroom will be slightly different because teachers and cultures are different but there are some things that are included in every Montessori classroom around the world.
The general sense of the classroom should be clean, tidy, airy and pleasant. Walls should not be too busy with posters and colours: the focus should be on the lessons. Materials, furniture & decorations should be real, not toy replicas. There will only some plastic. You will see glass, china, wood, silver, real vegetation, and, hopefully, an animal of some sort.
The classroom should have low, accessible shelves made of wood. Lessons will be neatly set upon the shelves in their respective learning area (see below). The lessons within an educational area will be placed upon the shelves in such a way that they grow in complexity from left to right taking into account room and shelving constraints. The photos below are from 4 different schools.
The typical Montessori classroom is divided into 5 educational areas: Practical Life, Sensorial, Language, Arithmetic, and Culture/Science.

The photo (found at http://mymontessorijourney.typepad.com/photos) shows part of a Sensorial area. You can see the Pink Tower at the extreme right, Red Rods, Broad Stairs, Sound Cylinders, and the three Colour Tablet boxes at the bottom left. The two baskets at the bottom right are extensions to the Colour Tablet lessons (the baskets at the very top are on the shelves of another section.)

Language Area - The Language area will have a mix of school-made and purchased materials but most will be the same from classroom to classroom. Lessons focus on the development of reading and writing. Typical lessons include: Sandpaper Letters, Metal Insets, Chalkboards, Classified Cards, Moveable Alphabet, Pink Material, Blue Material, Green Material.
The photo shows the Sandpaper Letters (just at the top left), Moveable alphabet (top right), as well as the Pink, Blue, and Green materials.
Arithmetic Area - This area will have mostly purchased materials. Lessons focus on the development of numeracy and mathematical understanding. Typical lessons will include: Long Rods, Sandpaper Numbers, Cards and Counters, Spindle Boxes, Golden Bead materials, Coloured Bead materials (Short Bead Stair, Bead Chains) and the Stamp Game.

Culture/Science Area - This area teaches about culture, history, geography, zoology, botany, and some basic science. Many lessons will be school-made but there will be a set of puzzle maps like the one shown, two globes (sandpaper and coloured continent) Other lessons will include "Parts of" cards (tree, flower, frog, turtle, fish, horse, bird), Clock, Life-cycle, Magnets, Colour mixing.

You can see better photos of individual Montessori lessons at this Montessori materials supplier (this is not an endorsement) http://ca.montessorioutlet.com/cgi-bin/category/5105