An LLC can decide if it wants to be taxed as a C corporation or to pass its income through to the members as an S corporation, a partnership or as a disregarded entity. If it elected to be taxed as a corporation then it would file either Form 1120 (C corporation taxation) or Form 1120-S (S corporation taxation).
If it chooses to be a partnership, it will file Form 1065. If there is just one member, he or she would report the income on his or her personal return (usually Schedule C if earned income or Schedule E if rental income) and would be a disregarded entity for tax purposes.
If a single-member LLC is owned by another LLC or by a corporation, the income would still be passed through to the owner's return, and no separate return would need to be filed for the single-member LLC. Normal monthly or quarterly returns would still need to be filed to report federal employment taxes, state sales taxes, and other periodic filings, just as for any other business.