Spades also has bidding without bluffing. Well, I suppose you could bluff by trying to intimidate the other players, but I don't think that's the primary reason for the bid. It hurts you to bid too high or too low.
Each round of Spades has 13 tricks. You bid however many you think you can take (if you have the ace of spades, king of spades, and the queen of spades, you are guaranteed to get at least three tricks). You can overextend yourself and bid too high since successful bids get you points, so higher is better, but I don't view it as bluffing. Arrogance perhaps. You might bid too conservatively and not realize that you have stronger cards than you thought, especially if you bid nil.