Aachen
If you want to know about Metal concerts, parties, etc. that take place in Aachen (and surroundings), you may want to check out this site: http://www.metal-aachen.de.
A nice pub for fans of Hard Rock, Alternative music and Metal. Often play Guns n' Roses, AC/DC and lots of good stuff from the 80's. Reasonable prices. Gets very busy, and has a large student crowd.
The Musikbunker consists of a pub and a small concert hall. It's actually not a Metal place, but there's the regular Metal Party every one or two months and a lot of Metal/Rock concerts, band contests and so on. Check their website for upcoming events.
Nightclub with an Alternative/Metal/Punk night every Thursday (starting at 22.00). Also some other Metal nights, check their website for the dates.
On the bar there's a sign saying Hard Rock Kneipe (Hard Rock pub) and that says it all. Sometimes live music.