Two toys worked well for me in the ferrets cage.  The first was a stuffed
baby rattle.  It's a stuffed piglet, acutally, from Winnie the Pooh.  It's
for a baby, so it didn't have any dangerous stuff glued on it, and the
ferrets went crazy when they heard the rattling noise.
 
The other thing I did was buy one of those springy cat toys- the butterfly
at the end of a elastic rope, etc.  I hung it from the top of the cage and
then amused myself watching them try to hide it in their blankets.
 
I don't know if you have the space, or the inclination, but the other thing
my boyfriend and I did was to buy irrigation tubing and make a maze around
the cage. We then cut two holes into the cage, and put the ends in.  They
love to tunnel through, and it makes me feel less guilty when we can't let
them out for a while.  We freaked out when we looked in one day and saw a
ferret missing, and it turned out she was sleeping in the bottom corner of
the tubing!
 
Have fun!  Ariel, Jasper, Taz and Bit
[Posted in FML issue 2302]