i second Spotlight, Plaza Singapura for sure! i just bought a bag of styrofoam ornaments (with the ribbon attached) and the kids painted them and then glittered them. every year i say NO MORE GLITTER (as i'm still finding it stuck in the rug)... and every year out it comes!
also try DAIKO on the 4th floor of plaza singapura - absolutely everything in the shop is $2 and you'd be amazed at all the arts/crafts in there. not your typical dollar store - it's all japanese and super funky.
you can also check out art-friend in nee ann city - great selection.