the best place is Muretto-KClub-Cafè del Mar , but it might be closed now (it is a summer cult).

in the centre there are no discos, only bars (go to the harry's bar and drink a spritz, this is a must!); the only one opened might be


Discoteca Casanova
Indirizzo Cannaregio,158/a 30121
Telefono 041 - 5240664

call and check out if it is open

Also, but a bit commercial/crap:
Discoteca Molo 5 Via dell'Elettricità 8 - Margheta(VE)
Odiami in Tessera -close to Etò in via Triestina sempre a Tessera(VE)

if u cannot renounce to a diso, try casanove or odiami plus molo 5, otherwise if u go around rom bar to bars drinking spritz and aperitivos u'll have fun anyway!