Astro-map
Interactive
A live model that links real astronomy to astrology. The Sun, Moon and planets are computed from genuine ephemerides, so any date is accurate to about a degree, retrograde loops included.
Scrub through time to watch planets move through the zodiac, the lunar nodes drift, and aspects form and dissolve. There's also a section on the precession of the equinoxes, which explains why the tropical and sidereal zodiacs differ.