The best on the market right now is the thermalright xp-90c, but if you want a 120mm fan (instead of the louder at equal power 90mm fan) you should go for the xp-120. The temp varies from person to person, it depends on many factors like you TIM or case airflow or the fan you choose for it ect ect ect, so it is impossible to know what your temp will be.
If you tell us what your system is, we can help you better.
edit: as much as I hate to say it the termalTAKE sonic tower is just as good, if not better, but its so big its scary.