I'm from Lübeck, originally. Although these days I spend most of my time in the city of my university.
My favourite club in Lübeck is "Parkhaus" (yes, it used to be a place to leave your car at). At Thursday nights you have the "Ladies Night". Now there are holidays for most students, so it should be full of young, beautiful girls. It's mixed music on Thursday, but mainly house and black music. On Friday it's not that full but still decent. Music is usually rock-pop, brit pop, independent. Sometimes they even have heavy metal and similiar stuff on a side floor. Saturday has a changing schedule, often big house music evens with popular DJs, though. The club is right in the inner city.
The other big club is the "A1". It has several huge floors and is really big in general. Music is black, house, techno, apres ski music. Depending on the floor. They have lots of Motto partys and there are always promotional events with cheap alcohol. Personally, I dislike that club, because they don't play my type of music, the club is too big for my liking and their policy attracts to many agressive people. But it's usually loaded with hundreds of guests, so there must be something about it
Then you have some other clubs. "Bunker" is a black/house music club, but I've never been there. "Hüx" is a very small club and usually very crowded place which looks a bit like 70s brothel from a movie. They play mixed music. Everything you can dance to, from ACDC to house music. You can find people from 16 years to 46 there. You either love it or hate it. It's right across the street where you also find the "Parkhaus". So I often visit both the same night.