The most eminent of the vampire houses is House Kheperu, which I believe was founded by Michelle Belanger (I could be wrong - if someone knows otherwise, I'd love to hear it). There are two reasons they're most eminent house. Firstly, because they published the Psychic Vampire Codex - the web-based and abridged version can be found here on Sacred-Magick, although it contains nothing of much practical use (unlike the full version so I'm lead to believe), it's a fairly good summary of Kheperian beliefs. I should point out though, that in the original Codex, the "counsellor" caste were actually the "concubine" caste, if that gives you some insight as to the mentality. And secondly, because Belanger helped to write up what is known as the Black Veil - a set of what was originally 13 laws for vampires to follow, although I hear that they've distilled it into less than that now.

Possibly the next best well known vampire organisation is the Vampire Church. I've never found them to be much of a resource though.

Following on is the Temple of the Vampire, who published the Vampire Bible - possibly the second most well-known vampiric publication. Oddly enough, I read a review of it by a Kheperian... and they found it to be rather egotistical, which amuses me since I find the Vampire Codex to be rather pretentious.

Possibly my favourite vampire organisation so far are the Strigoi VII who run the Sanguinarium. Although, like the Kheperians they have a tri-caste society, the reason I like them is because while they come off as a little insane. Not the "what a bunch of weirdos" insane though - the kind that you want to sit and listen to their ramblings, because you can tell that there's a lot of knowledge hidden in it.

A few other vampire houses (just to show you the diversity) are:
House Quinotaur
The Loyal Order of Saint Germaine
House Sekhemu
House Terebus
House Eclipse
The Darkness Embraced Vampire and Occult Society
The Court of Lazarus
House Crimson Blade
The Temple of Set with its Order of the Vampyre
The Order of Nekhbet
The House of Nephilim
The House of Dreaming (which I believe is Strigoi)

And there are plenty more. My most well-used resource is Sanguinarius, which despite the ads, is reasonably good - gives a few different perspectives on things.

A long time ago too, I came across a vampire court in both Sydney and Melbourne (the major cities outside Canberra, where I live), but apparently their sites either no longer exist, or I've just lost them.