In ES6, currently supported by default in Firefox and with flags in Chrome, you can do this:
a = {'a': [3,5,6,43,3,6,3,],
'b': [87,65,3,45,7,8],
'c': [34,57,8,9,9,2]}
values = [a[x] for (x in a)];
values
will now be the expected array.
This is also useful for code golf. Removing the spaces around for
cuts it down to 17 characters.