From memory (I have not lived there for about 10 years)
1. The first sunny day of spring walking round the Lanes and the North Laines watching to town become reborn after winter.
2. Going to an interesting pub, mixing with different types of people then clubbing and going to a house party and meeting even more interesting different people.
3. The eclectic music scene. Having the choice of so many different types of music across so many genres (often in one night).
This thread has me missing Brighton more than ever. I have still never found a town like it! BTID.