Romantic attraction is often indicated when the Ascendant of one person conjuncts or opposes another person's Sun, Moon, Venus, or Mars. Most potent when it comes to attraction are interplays between personal planets that are yin and yang, as these can arouse much intrigue. We consider the Ascendant as a yang energy, and exclude the neutral (unisex) personal planet Mercury.
These are the strongest interplays between personal planets and Ascendants. However, the yin-yang interplays tend to be more intriguing and "romantic". Of the planetary pairs in the list above, Sun-Venus seems to be the least sexual and romantic and instead it inspires a strong affection. Venus-Mars is probably the hottest sex and produces immediate physical attraction.
Venus-Mars conjunctions and squares can inspire quite a bit of fuss and sexual interest, while Venus-Mars sextiles and trines offer a more pleasing, less in-your-face attraction.
Venus-Pluto conjunctions, squares, and oppositions are one of the most potent cross-aspects for sexual and emotional attraction. Both people are attracted to each other, but it is the Venus person who is obsessed with the Pluto person. Venus is consumed with the attraction. Ultimately, it is the Pluto person who has the upper hand in terms of whether the relationship is going to endure.
Mars-Sun conjunctions, squares, and oppositions usually inspire a need to make the relationship physical between you two. Trines generate some physical attraction, but of a more pleasant kind.
A conjunction of someone's Mars to your Ascendant, Descendant, Midheaven, or opposite the Midheaven will pull out gut reactions and intensity of desire. The feelings can go either way.
Connections that seem fated and karmic often include conjunctions to the Vertex, especially personal planets or the Ascendant or Descendant, opposite the Midheaven, South Node, and the Vertex or Descendant.
Midpoints in Attraction
The Sun/Moon midpoint is very often activated by the other person's personal planets in significant relationships. The Sun/Moon midpoint represents a point of "inner marriage" and symbolizes close personal relationship. If another person's personal planet, and especially the Sun or Moon, forms a close aspect, that person represents some kind of promise of integration. Whether or not integration actually happens, this connection offers a promise which can be difficult to resist. This makes it a strong indicator of attraction.
Attraction does not guarantee longevity, of course. It generally does precede a significant relationship, and in some cases, is important simply for what it is, as we may not have a current interest in establishing binding ties.