<< meditation beads >>
Like they mentioned above, they are meditation beads or prayer beads. Most people who actually use them for purposes other than decoration will chant a sort of mini-prayer and each time you chant it, you move your thumb to the next bead. There is usually a tassle like string attached between two of the beads on the necklace which is used for counting purposes (much easier to count the number of times you've gone through the entire necklace rather than each individual bead)
BTW, just go to your local Chinatown for a set.