Easily accessible by Public transport:

Regular Events

Lange Nacht der Museen (10 Min.) at March/April
Porsche Tennis Grand Prix (10 Min.) at April
Stuttgarter Frühlingfest (10 Min.) at April/May
Waiblinger Altstadtfest (10 Min.) at June
Mercedes Cup (20 Min.) at June/July
Hamburger Fischmarkt in Stuttgart (10 Min.) at July
Jazz Open Stuttgart (10 Min.) at July
Stuttgarter Sommerfest (10 Min.) at August
Remstal-Klassik (10 Min.) at August
Stuttgarter Weindorf (10 Min.) at August/September
Volksfest Stuttgart (10 Min.) at September/October
Fellbacher Herbst (5 Min.) at October
Stuttgartnacht (10 Min.) at October
Stuttgart German Masters (10 Min.) at November
Stuttgarter Weihnachtsmarkt (10 Min.) at December

Current Events

Rocky. Musical at SI Centrum Stuttgart (20 Min.)
Tarzan. Musical at SI Centrum Stuttgart (20 Min.)

Other events in the region of Stuttgart can be found here.