Go to a post office (if you are in Japan) they have machines that they will put the coins in. The machine calculates the value of all the coins, and they'll give you back cash.
Sumitomo Bank ATMs take coins. I sometimes save up all my annoying ichi en coins in a little bottle in the kitchen and take them down there (outside of peak times of course). Bang! A sen yen beer token and my wife is none the wiser when I buy the posh beer.