I assume you're doing a partial boil; what I do is pre-chill my top-off water in the freezer (in gallon jugs) while I'm boiling my wort. Once the boil is finished, I put my pot in the sink with cold water to cool as much as possible, then put a gallon or two of my top-off water into the fermenter first. I like to shake up the jugs to provide aeration for the yeast. After 5-10 minutes and the wort has cooled somewhat, I pour it into the fermenter on top of the cold water. If I'm still under my target volume (and over my expected SG), I add more cold water to reach the right level. Usually this puts my wort temperature at 70 or so and ready to pitch yeast.
If you're doing a full boil, you'll have to cool the whole pot before it goes into the fermenter. Most folks use a wort chiller of some sort to speed up this process. Either way once the boil is over you want to cool that wort down to 70-75 as quickly as you can.