Here is a list of rental sites :
http://www.habitat-property.com/web%.../page/home.asp http://www.landmarkasia.com.hk/ http://www.hongkonghomes.com/hong_ko.../eng/for_rent/ http://www.proway.com.hk
Where you'll be, how big it is, etc etc will all depend on your budget...
As Jimbo said, there are some nice serviced appartments in Hong Kong, where you can stay as long as you like until you find a place. One I recommend that's away from the city is De Ricou in Repulse Bay, because it's in front of a beach, and there are many convenient facilities : gym, pool, cafes, restaurants, supermarket, drycleaning, doctor, dentist etc. but there are also some good ones in town.