I have enjoyed BENT TAP-X, Placette RVC (and Active Buffered), K&K S&B Transformer, Goldpoint passives. The best of the lot in an ideal set up has been the Lightspeed Attenuator (LSA). As Clio9 mentions, not all situations are ideal in terms of impedance (usually, but not always ok in terms of gain) and you would need to use a buffer - like those mentioned by Clio9 - First Watt B1 and The Truth, or one of the above mentioned along with something like the Burson Buffer. These solve a problem, but the best passive aproach is with no buffer when you don't need one. Your setup is borderline and you don't mention the lenght of your IC cables from passive to amp - another consideration.
I don't know about Stringreen's comment, other than I know many folks that have used several 5-10K preamps that swear by passives - so not a complete waste of time and money for some - certainly not for me.