Beers focussed: Braustüb'l (Darmstadt brewery) Shite beer better off trying for a Pfungstädter pub. They also have a second pub in town, Ratskeller (has own brewery) also shite beer but you can make a good evening of it by ordering a barrel and serving yourself. Rather touristy during the summer, An Sibin used to be good when it opened and then got overrun by septics and the prices went up. Went there a while ago and the prices seem back to normal and was a bit more atmosphere. Rather large as it used to be a Kegelbahn, Sitte (Pfüngstadter) restaurant, Grohe owned by the Darmstädter brewery. Go there now and again but it tends to be an oldies pub. Drinking lots of the beer will give you a hangover. Bars: Weststadt (my friends all seem to love this place, but not my cup of tea) posers, Chaos (versatile, almost everyone of a certain type goes there sometime), Aussie Bar (not an "ex-pat" place) went once, never again.
Just my opinions...
Zum Landgrafen used to be the in place for Brits but has gone downhill but you can still get a good beer there. Whenever I go in with my friends the landlord always puts good music on (he used to be an old hippy and you can see a picture of him when he had hair - he's bald as a coot now
KupferKessel - good beer, Apfelwein from the Odenwald, food from Metger in the Odenwald, speciality is homemade Tequilas of different flavours (i.e. Mocha or Chili) Always shows the boxing. Rather a mixed crowd, used to be a hang-out for bikers but has changed a lot recently. Not for everyone
Green Sheep - Reasonably good beers, food ain't bad either. Live music and a rather good selection of whiskeys
Riwwelmaddes - excellent food, Guinness is very good, other beers not so good, older crowd
If you want to pick up women (not girls) then try Caribe. This used to be a disco called Hippos and they've started doing revival nights for old times sake so the crowd is older and a bit looser (mind you the disco in the Krone is always good for a laugh.)
If you really want, you can easily drink in Darmstadt 24/7 you just need to know the pubs (i.e Hercules)