As a secondary (supplemental) hash, I found the Murmur finalizer methods are ok, but you can get better if you use different constants. See my result in this answer: https://stackoverflow.com/questions/664014/what-integer-hash...

I measured the avalanche effect (the number of output bits that change if a single input bit is changed; should be nearly 16 on average for a 32 bit hash), independence of output bit changes (output bits should not depend on each other), and the probability of a change in each output bit if any input bit is changed.