Formation state
Delaware is the most common formation state for founders coming from outside the US, followed by Wyoming. Each state has its own annual tax or report; the US federal 5472 obligation is the same regardless of formation state.
Default tax treatment
A single-member LLC is a disregarded entity by default. It has no separate US federal income tax return (no 1120, no 1065). The owner reports the LLC’s income on their own return.
What changes for a foreign-owner SMLLC
See the 5472 entry. The LLC becomes a corporation for information-filing purposes and files 5472 attached to a pro-forma 1120.
Electing out of default
An SMLLC can elect to be taxed as a corporation by filing Form 8832. This is rarely useful for a non-US founder of a passive LLC, but it does come up — and it changes what you file every year.
See also: disregarded entity, multi-member LLC, Form 8832.