From Diablo Wiki
Fans have occasionally asked if whips will be a weapon type in Diablo III. The answer thus far has been "no," though the D3 devs don't seem to be ruling it out in principle, as they have done with guns. Whips will not be in the initial game; if that weapon type was going to be added, it would be in already. If we see whips as player weapons, they'll be added in one of the expansions
Whips do exist in the Diablo world -- theuse them in Act Two of Diablo II, as fairly slow, short-range melee weapons, so the concept is not entirely foreign to the game.
Blue Comments on Whips
The whips question came up again when the Demon Hunter was revealed at Blizzcon 2010, since the style of that class seems to go with whips, in the minds of some fans. 
Every time the topic has come up, it's been from a fan asking about it in the Battle.net forums or via @Diablo's twitter. Fansite forum threads devoted to this weapon type aren't unknown either.
The main objection to whips is that they are unrealistic. After all, it's a weapon used to cut unarmored opponents, or else in one-on-one combat as a way to lasso an opponent's arm or otherwise put them off their balance. As such it doesn't seem that fitted to the massive hordes of heavily-armed enemies that characters battle in Diablo III.
On the other hand, it's often pointed out that most of the weapons and spells in Diablo III are "unrealistic" in one way or another, and most of the complaints about the whip could be extended to daggers, light clubs as melee weapons, etc.
Common suggestions for whips is that they would have a very fast attack rate, and be more effective from a distance, with a stun or perhaps double hit possibility. It's not known if Blizzard has given any thought to how they might implement this weapon into the game, but fans enjoy the discussions.