Singapore is fantastic - so much variety on one island. Still areas where it's very similar to what it was like 40 years ago, and then other areas that weren't there 10 years ago (Marina Bay). Getting around by cab or MRT is easy. There's some great walks through parks etc around as well as all the shopping, theme parks etc.
Chiang Mai around northern thailand is great as well. Went in September last year, airfares from singapore, four days/four nights stay with all activities (kayaking, mountain biking, hiking, cooking school, coffee shops, zip lining), driver and transport in private van with five others in our group, accommodation, all meals (not including alcohol), came in at $500 AUD per person. Loved it, were three kids on the tour who all had a blast. Can't wait to go again.