For many people, the topic of high IQ or the high IQ society is associated with a negative stigma of pretentiousness and elitism. Questions arise such as "why would highly intelligent people need to converge other than to boast about their superior intellects or discuss the inferiority of the masses?" As a veteran of the high IQ community I can assure you that while there are a few enfants terribles in the crowd who like to peacock their abilities (just like any other social dynamic), most of us are just looking for high octane, good quality conversations with those who share similar interests. It's a known fact that communication begins to breakdown when the difference of IQ spans greater than 30 points (see Hollingworth) and those with similar levels of intelligence will be drawn to each other. However, the brighter the individual the rarer the chance of meeting these people, hence the need for the high IQ society. Below is a detailed list of several societies along with the IQ requirements. For more information regarding these high IQ societies, read Bill Bultas' detailed reviews here. Another excellent site (highly recommended) is the Uncommonly Difficult IQ Tests page. 

95th Percentile (1 person in 20):

International High IQ Society  

98th Percentile (1 person in 50):

Mensa

99th Percentile (1 person in 100):

Intertel

Top One Percent Society

Mind Society

Elateneo/s Society

99.5th Percentile (1 person in 200):

Poetic Genius Society

99.9th Percentile (1 person in 1,000):

ISPE (International Society for Philosophical Enquiry)

Triple Nine Society  

One-in-a-Thousand Society

Glia Society

Ludomind Society  

Milenija

Genius Society

ISI-Society

CIVIQ

99.997th Percentile (1 person in 30,000):

Prometheus Society

Epimetheus Society

Camp Archimedes Society

HellIQ Society

99.9999th Percentile (1 person in 1,000,000):

Mega Society

Omega Society

OlympIQ Society

99.9999999th Percentile (1 person in 1,000,000,000 - controversial):

Giga Society