Bars
Fiszbah
Legendary little dive bar with hot waitresses, cold beer, interesting people and wildly diverse music e.g. "Discopogo for Punks in Pumps" on Tuesdays. Limited food menu and breakfast/brunch on weekends as well.
Hafeneck
Neighborhood bar that manages to simultaneously cater to football fans, local hipsters and an endless streams of niche musicians ranging from the "Whiskey Rabbi" to Vicky Vomit. The kitchen open 5-11PM daily also serves up huge salads, a few German classics like schnitzel, plus giant savoury pancakes Eierpfannkuchen with unusual fillings, many of them vegetarian — try the "Hades" to add some spice to your life.
Pubs
Eisgrub-Bräu
55116 mainz weissliliengasse 1a, (http://www.eisgrub.de/). this cavernous "ice cellar" has brewed its own beer since 1872 and is still packed most nights. in addition to their own beers, pale and dark, they also serve up hearty portions of honest german grub.
Mainz Kastel Brauhaus
Located on the otto suhr ring road wiesbaden mainz-kastel, 2 blocksright off the main hwy b455 going to wiesbaden, from mainz across the theodore heuss brucke-1k. you can see the biergarten's umbrellas using google earth. it is the german equivalent of an american microbrew pub/restaurant. their light hell beer with mainz's famous spundekase and pretzels is great. well worth the visit.