Manipulatives

I am not in the classroom right now so I am not using manipulatives.  I use things around the house to help my kindergartener and 3 year old learn one-to-one correspondence, and how to count up or add on, but nothing formal.  When I was in the classroom I used fraction tiles, unifix cubes, geoboards, etc.  All the basic stuff.  Now I am hearing about the virtual manipulative online and I would like to learn more about that before I go back into the teaching world.