I think all but 5 states have laws dictating pay frequency, and in most cases they require at least two times a month pay frequency.
The most popular pay schedules tend to be 24, 26, and 52 times per year.
EDIT: This was supposed to be a reply to redblacktree. State law examples: - http://www.dir.ca.gov/dlse/faq_paydays.htm - http://labor.ny.gov/legal/counsel/pdf/frequency-of-pay-frequ...