Something I forgot to mention: one thing students in Münster know is when to go where for cocktail happy hour :-)
One of the great places is Enchilada im Lortzingsaal. Wonderful high ceilings, nice beer hmm cocktail garden, packed with people and music and smoke and fantastic cocktails!
They also serve Mexican food but you need to reserve a table for that!
cocktails (quite pricely outside happy hour...), texmex-food, loads of students (upperclass ;)
highly recommendable in summer, sipping Caiphirinhas on the terrace is a nice way to spend a night.
best night: wednesday
Dress Code: none, most of the guests are more upperclass, but no-one really cares.
For me, Munster's nightlife consisted of eating Yemeni food with Yemenis and talking until the small hours with Yemenis and the odd Moroccan. I would imagine you won't experience this on your visit to Munster!
The traditional consert with the Dubliners before Christmas is highly recommendable... Nice atmosphere in a place called the Juvel, which normally is a bad disco for kids from 16-20. So don't go there if it no special consert going on..
Cavete, 'akademische Bieranstalt': a studentspub.
This pub is since 28 april 1959 run by students and for students. You can start teh evening with a simple but nice meal and chat the night away over an Altbier. Speciality (in Munster): Altbier mit Schuss, a reasonable quantity of sirup added to the beer. Not my cup of tea...