We've always appreciated LEGO's versatility but seeing it used as a mathematics tool really caught our attention. With just a few of the simplest of bricks you can make a dynamic math worksheet.
Simply add the 'bumps". To learn a bit more on how Mary-Ann of Counting Coconuts put it together pay her blog a visit. Browse around her blog some more and you will find all sorts of Montessori-inspired learning activities.
(Images: Counting Coconuts)
100 DIY Ideas for the 3-Day Weekend
Danielle's Charming, Classic Walk-Up
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
White Enamel Flatwa...
How To Cook Fluffy, Tasty Quinoa
Perfect Summer Cocktail Recipe: Honey Bourbon Lemonade
Lego Duplo also makes alphabet letters which are my kids love http://shop.lego.com/en-US/LEGO-DUPLO-Play-with-Letters-Set-6051 (retail version)
http://www.legoeducation.us/eng/product/letters_set/1473 (from the education line)
I home school my oldest son after a difficult 9 years of public school and we use Math-U-See for his mathematics. It uses Lego style blocks from the very beginning. The idea being that you can see why the math works. I admit, I've learned a lot about why things work that I didn't realize I was missing just from using blocks. (Note: he's doing GREAT!)
This is just the thing I've been wanting to do with my Lego fanatic four-year-old!