A friend of mine told me about 2 bars, not in Sachsenhausen (where we were last time) - one called "Jazzkeller", should be a pretty cool pub - with jamming every wednesday...
Sounds cool and I should not have posted that, because I just looked it up - they are closed on 6th because of some private event.
Other one "nachtleben" seems to be a combo of concert-hall and bar next to it - I can't find any more info, only the homepage of the concert hall:
Another bar seems to be around Eschenheimer Turm, some "scene bar" - doesn't even have a name.
Last but not least there's some stuff in Sachsenhausen left, if we can't decide or find a place to stay. I'm coming wednesday afternoon, a little too late to do some scouting of the bars previously, sorry.
I'll look for some more locations, a lot of people told me Frankfurt in the city is not too good - more the outer areas and towards Darmstadt - but I don't think we should have to take such a trip. A place with beer should be enough for a good time with you guys!
BTW: If someone finds a cool place or Flo, if you want to make a reservation in a bar or something - just tell me, I've no problem calling them.