I haven't personally been to many festivals because of my young child but there are quite a few that come to mind which are worth checking out. Nothing better than a recommendation from an avid festival-goer!
The first one that comes to mind is the Singapore Food Festival, held every July. It's a month-long celebration with plenty of food options including local and international street food. They even have workshops where you can learn some cooking techniques!
There's also the annual Sundown Festival at the city's largest park, East Coast Park. It's a real fusion of cultures, with tons of food options and live performances going late into the night - think indie folk to rock. It's super vibrant and lively, definitely a unique experience.
If you're up for a cozy, quirky one-day event, there's York Fest at York Hotel. It's a relatively small scale festival with a charming, intimate vibe, but what it lacks in size, it makes up for in its quirky, artsy performances and activities. They've even got a "silent disco" corner, which is a hoot! And of course, lots of tasty treats to discover.
These are the ones I'd recommend, but there's so many more out there! Hopefully, some other forum users will chip in with their top picks.