One thing relating to psychology I know I will never forget is the idea of "better dating through science", both the biological and emotional implications of the psychology behind attractiveness and relationships.
I saw this great documentary, The Science of Sex Appeal (which can be found here or here.) on the Discovery channel last summer, which is all about, you guessed it, the science behind what makes someone sexy and why some people find others more attractive. Being the nerd I am, I was completely engrossed with the findings, material, and social experiments in the program (I seriously recommend it to everyone). So when chapter eleven came, I was really happy to find out I already knew that portion of our textbook and discussion section.
I know I will remember this five years from now, because ever since I saw that documentary, I haven't stopped making really sarcastic comments when my friends are watching romantic comedies (such as how the female protagonist only finds her opposite attractive because his face is symmetrical, thus meaning he has good genes, or because he happened to meet her when she was having a hectic morning, so the rush of dopamine forever influenced the fate of the movie).
But in a more useful and less cynical sense, I've been using this area of psychology to try and look at my own and other's relationships more scientifically. Human behavior sometimes makes a little more sense, now.
So thanks for all of the tips, Psychology!